I wish I could muster quite the same high level of enthusiasm that many online reviewers seem to have for this property.
It certainly has tons going for it: a sprawling and beautiful campus, gorgeous design, well-above-par hard product and a talented, kind staff.
We enjoyed ourselves immensely during our stay.

It was simply bookended during our 10 days in Morocco by two other hotels that easily surpassed it, and on nearly every level.
And one of those hotels was decidedly less expensive as well.
(You can read my review of that hotel, Olinto, as well as Royal Mansour).

PLUS POINTS

I will touch only briefly on Mandarin Oriental Marrakech’s manifold highly-recommendable attributes.
These plusses are noted in many FT comments/threads/subs, and i agree with just about all of them.

Our plus points, in order:

--The grounds are gorgeous.  Common spaces, pool(s), spa, landscaping, placid water features, a really great kids club..... everything is designed to exceedingly high standards.
The overall effect is one of beauty, tinged with a refined/tasteful drop of youthful energy, family fun and ‘buzz’. (It’s not a W or DIsney Cruise or anything even close to that, mind you, but this place definitely has a contemporary fun vibe, and across the board - design, music, clientele, food, furnishings, all of it)

—Special mention for the spa.  Wife says it's one of the best spas she's enjoyed.  She says top 5-10 all time, in fact, and that’s high praise coming from a bit of spa-soldier.  I spent time in there too, and it is a truly breathtaking facility.  We had a hammam and it was extraordinary, as well as a couples massage.

---Service is exemplary.  The Gm here had high praise from several trusted FT advisors, but he was not on property during our low-season stay.  No matter, there was another, young manager named Christophe, who is a gem.  He runs a fantastic service operation here.  All staff are gracious, unassuming (zero ‘airs’ or fake smiles), and all work hard to make one’s stay perfect.
They didn’t succeed fully for us (see below) but everyone here is a total pro.  Note, we made a few fairly obscure requests - "do you have a heating pad or hot water bottle?"  - and they were all fulfilled within an hour or two.

—F&B generally good.  We're not gigantic foodies, but this place more than satisfied us.  Breakfast at Shirvan was excellent all three days.  Huge buffet, to-order menu as well.    There’s also Ling Ling, where we enjoyed two dinners.  It’s pretty darn good - and the dining room itself is a stunner - though not quite as knockout sublime as we expected from a Hakkasan kitchen.   Pool restaurant has some hiccups w service (not comportment at all, more wait times, coordinated delivery, possible understaffing?), but lunch food there also very satisfying and tasty.
We’re not the pickiest cocktailologists or wine people, but the drinks we had at MO were fantastic.

—Villas are stupendous. Ours, a 1BR, was one of the most jaw-droppingly beautiful room products I have ever seen.  It really is something, whether one considers sheer size, layout, design, furnishings, or any other single attribute.  I'd read all about these villas, and still i was not prepared for how spectacular they are. A mesmerizing interflow of indoor/outdoor space, totally private, pure luxury.

Until….. it gets to infrastructure/systems/bells-whistles.

Still, if you don’t care about infotainment (or don’t want to watch/listen to it on anything larger than your own self-provided phone/laptop), and aren’t easily flummoxed by complex control systems for lighting/electronics, then you might very well say it’s among the best hotel rooms you’ve ever slept in.

MINUS POINTS

In order, first being by far the biggest, but all adding up.

—“Infotainment” -
This is what really brought this 3-night stay down for us.  It's frustratingly ironic, and the irony exists on two levels:
1) It wasn't really a tough blunder to recover from.   (Nor a particularly expensive problem to solve if the same problem exists in all or any other villas).  Still, MO was not able to fully recover here, in our villa, with three separate attempts in three days.
2) The problem (nearly) killed what we found to be the single best attribute of this hotel - the villa itself.  It’s like they baked the world’s most delicious cake, and iced it with plain margarine (or skipped the icing altogether).
Granted, not everyone is vapid enough to fork over this kind of $$$$ in an exotic locale and retire to HBO or Netflix at 9pm most nights. But we do.  Especially when we're in the middle of a decent show (on this trip, ‘The Diplomat').
Our villa had a great-looking 70-80 inch LG affair in the living room, and in the bedroom a 30" inch TV that rises out of a panel at the foot of the bed.
So far, looking good.
Awesome on the LR television! 
And...well... whatever on the smaller BR television (the Houdini-rising thing is an old parlor trick we thought silly when we first encountered it in Ravello a decade ago, but still, it's a flatscreen….)
On both of these TV’s, we had the choice of watching the following in English:
1- CNN international news
2- BBC world news
3 - Mandarin Oriental's own hotel-info channel, and.....

That's it.
No other English programming or networks.
No menu of PPV movies.
No streaming apps.
(Seriously, over the last 8-10 years, have you stayed at even a Best Western or Ramada Inn that didn't at least have some Roku or apps on their tiny smart TV?).
Endless TV channels and networks in Arabic, French, Berber, Turkish, German, Italian, Greek, Polish, Russian, Hebrew, Mandarin (of course), Japanese, Swahili, Hindi.......
Two networks in English.
Running exactly the same (depressing) news items.

First night:
The TV says (and MO claims) it's got Appleplay via wireless built into it, but it wasn't working on the first night we tried to link up with my Macbook Air. .  I'm pretty good at this stuff - work in media for a living - but whatsapp'd the butler.   He comes by and can't get it sync'd to his iPhone.  IT person comes by, he couldn't get it linked up with his laptop either.
They then told me they'd bring a straight USB-c to HDMI cable so i could come directly out of my laptop into the tv HDMI.
I was delighted, and apologized for not bringing my own.  (I really should have).
The cable they brought that second afternoon (while we were off property) worked when they were there, so they said. (They left a really nice note that said they at least got my Apple sign-in/password page up on the big TV.)

Second night:
We got back from dinner at Oberoi round 10:30pm-ish to fire up ‘The Diplomat”.
Worked until about 8 minutes into the show and then….
The entire TV froze up. Couldn't do a thing with remote or buttons on the tTV, had to unplug from wall. Turned back on and the cable did not work into HDMI input at all.
What'sapp the butler (he's gone, see below) but concierge responds.  I call her up.  She saydthey'll bring an Apple TV box the next morning - i lightly protested that all i really needed was a smart tv; that i'd even be thrilled with a much smaller tv if it had internet capabilities.  Surely at a property of this size, they have some newer tv's boxed up somewhere? Or a tv in an unbooked room or conference room they could move? And again, I'm fairly OK at troubleshooting these kinds of things.
Me: "It seems like the HDMI port on this tv may be messed up. That combined with the non-functioning of the Appleplay and the freeze-up yesterday indicates this TV might have a deeper root problem than connectivity or ports.... more like a power-supply issue or a motherboard failure…."
Said very nicely and respectfully, but realized i was talking to a concierge assistant at 11pm.
"We think a separate appleTV box will work much better!"
Okie doke.
They left an apple play box and of course it didn't work on our last night.

Third night:
We watched an episode of ‘The Diplomat' on my teensy Macbook Air, balanced at the foot of our bed where the TV exhumes itself out of.
Like i said, irony.

—Another, far less problematic but still frustrating issue in villa was a needlessly complex control system.
The villa is silly with (beautiful) lighting. Light fixtures everywhere. Some in pairs/sets, some not. Some floor lamps, some suspended lighting, some soffited ceiling lighting, some wall sconces, some 'night' lighting built into floors, a pair of night-reading pencil lights in the headboard….
When some or all of these lights are illuminated in various combos and brightnesses, i'm sure it must give off some very sexy and flattering lighting. But the controls seem dated, even for 2014 when the hotel was built. Not unresponsive 'touchpad' screens, thank goodness. Almost as bad, though: an array of interdependent switches and knobs and sliders of all types. Some were quality metal, military-grade on/off switches, very satisfying to switch. Other switches were cheap, plastic see-saw type like in my house at home. Same function - on/off - why the different switch types? For others there were knobs and faders for brightness (some of those knobs and faders clicked 'off' at lowest value, while others didn't). All of these various controls are labeled in sensible ways (theoretically, at least), yet somehow little of it worked the way it read on its label. And turning or switching one thing often seemed to have an opposite ghost-effect on another type.
Example, in the bedroom, for whatever reason, the TV-rising button also controls drawing the heavy blackout drapes.  The heavy blackout drapes have their own independent open/close switch, mind you.  But those drapes are also inexplicably tied to the TV up/down.  (Which does not have a truly independent switch of its own).   
So.... if you get them out.......of............sync...........................
In this way, we spent a not insignificant portion of our villa-time trying to sleuth this stuff out.

—There is a side/butler’s entrance for our villa that was completely open for half our stay.  This was mere steps from our villa’s properly-secured main entrance, and on the main path.
It wasn’t just unlocked, the door itself couldn’t be clicked into a ‘closed' position at all. 
It was fixed by the end of our 2nd night.  And we’re not big security freaks.  But at these rates, you can be sure this property sees its fair share of diplomats, moguls, athletes, rock stars, celebrities, etc, and you can be sure that THEY would have found this situation, um, concerning.

—The ‘doorbell’ on the villa isn’t really a doorbell.  It rings the phone inside the villa.  With the same kind of "phone-is-ringing" tone, leaving the villa occupant unsure who’s calling, whether someone’s ‘calling’ at all  - front desk, valet, housekeeping, room service - or someone standing outside your villa.  Result?  The phone in this room rings a LOT, and it’s not the most pleasant sound ever.

Outside the villa, we found a few other minor issues

—Mandarin Oriental Marrakech is still stuck in a time-loop from decades ago when it comes to signing bills.  I reckon i signed my name to a bill at least 8 times within any single day/night cycle that we spent on property.  Maybe more.  And we spent twofull days off property!
You must sign for every last transaction that happens between you and MO.  Every car transport, every drink, every meal, having you villa fire lit, anything from the outside world you’ve asked for from the concierge (down to batteries, cigarettes, tampons), all of it. 
Even tiny room service items beyond food. (sunscreen).
We found it rare to have any interaction with any MO staff besides pleasantries/salutations that didn’t also include writing down our room # and giving our signature.
I’m not sure why this is. Yes, there would normally be an opportunity to give a tip/gratuity under such circumstances.  But MO lets you know on check-in - as they do at several other of their locations, as do many fine hotels everywhere - that while tipping is certainly 'not expected/always appreciated', 'all tips are split evenly between service employees', and 'you can add a single gratuity amount to your final bill should you wish'.
So why the constant signing?  Besides being a pointless extension of what's already - purely by definition - an 'interruption',  why would any hotelier want to be constantly reminding patrons how expensive everything at their hotel is?
I’m used to signing for room service, full meals (not always that) and not much else at upscale/luxury hotels these days.

—Even as we had our first hotel provide transport from RAK, Mandarin offered us complimentary 'fast track' service at the airport with our room.  We gladly accepted.
They did not set it up.  We ended up having to spend an extra 45 minutes at RAK, with someone at customs on the phone with MO sorting it out.  Not the best way to start a 2-week 20th anniversary holiday.

—Some basic missteps with food orders, wrong thing brought, items forgotten, etc. Mostly at pool restaurant, but wrong cocktail at Ling Ling as well.

—This is a small point (I'm an audio person, for sure) but i noticed there is a perpetual sound/music ‘fight’ happening on the main communal grounds. All day, but especially noticable at night.   Walking along the ‘main drag’ after sunset results in a melange of no fewer than four distinct music styles/tracks.  Not in a row, mind you, that'd be more cogent..... there generally play all at once and mix together.   It’s not loud, but it’s definitely cacophonous/atonal.
There is one style of music playing allllll around the main space and water features, w/small speakers at knee level, every 10 feet or so, facing out towards the surrounding walkways - this is very pleasing, chill-zen beats type music.
Ling Ling (with speakers also facing outward towards the pool and walkways) plays slightly more upbeat club-y type tracks. At slightly higher volume.
Next to it is Shirvan, playing various styles, mostly quiet Moroccan, SOul, STax type music.
Then there’s the party/bar-tent which plays full-on bar/dance/club music, and quite loud..
All of it is great on its own, well-curated for the individual settings and none of it is ever obtrusively loud. 
But at night, if you’re not in your villa, you’re essentially hearing a faint background of three or four different pieces of music, all at disparate tempos and in various keys.  Interesting to the ear, but not always pleasing.

—Like many other top-end hotels, MO provides a ‘butler’ for your stay.
I continue to question the necessity both of this name (kind of demeaning) and, really, the role such people play.  I get it for large families with young kids, or elderly couples, or people who need real help unpacking.
But in our experience, other than providing a first-day tour of the room/property, they are usually simply a dedicated human on the other end of what’sapp or the telephone. 
Really not unlike what most other hotels have called a ‘concierge’ for a very long time.
Our dedicated concierge was named Ahmed (Ahmet?) and he was just as nice and professional as every other staff member we encountered here.
However, he was only 'with us' for two of our three nights onsite.  The second night, he told us he was leaving, and from that point on we simply had the hotel’s concierge desk replying on the other end of his what’sapp #.
Not at all a problem for us; again, we don’t need a butler.
It just seems odd: If you’re going to proffer (and more to the point, tout) a dedicated butler for each villa, seems reasonable for the guest to expect the same person in that role for the entirety of their stay.   Particularly on a comparatively short, midweek, 3-night booking during low season.

CONCLUSION

Mandarin Oriental’s management, staff and physical resort provided us with a great four days.
It is undoubtedly a fine hotel, if not quite at the level of a few other MO's i've experienced (Milan, NYC).
Still, it is among the very highest-priced resorts in the extremely competitive (some might say oversaturated) Marrakech luxury market.  And we weren’t able to end up enjoying our room nearly as much as we might have liked.
For this and a few other problems we mentioned, Christophe offered to pick up one of our Ling Ling meals.
Given the advance booking, nature of this special occasion, blown FastTrack coordination, and the persistence of our villa problems, though, i thought comping one of the room nights would have been more appropriate.

Even had our stay been perfect, though, our overall thought in retrospect is that this hotel might be slightly better-suited to younger couples than us (we’re mid-50s) for romance, or families for fun, than for what we wanted on this trip. We visited several other Palmerai hotels during our 10-day holiday, and thought both Oberoi or Amanjena - as two examples - might have been a more appropriate choice for our purposes on this particular trip.

Room

Dining

Overall