I'm a HUGE fan of IHG Diamond! All things considered, my Diamond/Amb experience is now better than it was when I had RA status 2006-2015 or so. At the time, RA typically got either club access or an upgrade (often suites, but some hotels playing games, still fondly remember that "executive" room with fax machine at Mark Hopkins), no breakfast, and no benefits on award stays (which some hotels granted in spite of the rules). Had only a handful of IHG nights annually during the Spire years, with 150+ going to Hyatt and Marriott. That changed completely; still going to hit 100 this year with Hyatt (but only because their limited footprint happened to work well), but only 16 nights with Marriott (relying on LT Tit for the handful of times Marriott is the best/only option), and 80ish with IHG.

Positives:

• I generally get meaningful upgrades, often far more than 1-2 categories. Still doing a bit better with Hyatt, but IHG is far ahead of Marriott, where LT Tit often gets you nothing ("we have 6 Ambassadors, 16 Tits, 34 Plats and 45 Golds arriving today, so enjoy your high floor room and access to our overcrowded lounge").
• The breakfast amenity choice is adhered to by all hotels without question and in most cases quite generously -- it's always access to the full buffet (or whatever the hotel's restaurant offers to paying guests). I have not encountered any ridiculous rules, which are common with Marriott (depening on brand, sometimes continental only, sometimes $10 dining credit, sometimes the guest has a choice, sometimes not, etc etc). I'm not much of a breakfast eater and often skip it, but huge thumbs up for IHG for implementing this so well!
• I occasionally travel with family, and booked a second room on ~a dozen stays. I don't expect this above-and-beyond generosity, but 90% of the time, benefits are extended to both rooms (upgrade, breakfast and lounge). Hyatt does this, too, alhough it's more formalized (I often use a GOH or club pass for the second room).
• I love the Lounge Pass. IHG and Regent lounges are generally superior to those at Marriott and Hyatt. I had anticipated that this generosity wouldn't last, but I haven't seen overcrowded lounges, and my fears of separate lounges for Lounge Pass holders (with reduced offerings) or other enhancements of this milestone haven't materialized. I also didn't notice any widespread scaling-down of lounge offerings. That said, I applaud the changes IHG implemented to minimize gaming by making sure people couldn't get Lounge Passes for 2 years by making the selection on Jan 1st, and I'd like to see the Lounge Pass option only available at 70 nights.
• Points earning can be pretty spectacular, and there are generous and reliable cashback options available for IHG. With stacking promos, I often earn 30%, sometimes 50% of my spend back in points and cashback. Hyatt is abysmal on this, and Marriott not great.
• Since this thread covers a review of the past 3 years, I'll list redemptions as a major plus. It's unbelievable what values I've realized over these three years. $100 worth of points for a night in Tokyo or Phu Quoc over NYE is quite sweet. Now, a lot of these were due to the initial program switchover glitches (27k night for all ICs, IIRC) and the end-of schedule glitch still worked for some properties throughout 2024, even though it's now uncommon. Of course it helps that I'm fairly flexible and generally spend 4 nights, so I'm able to take advantage of the Chase 4th night free benefit.

Negatives:

• Outstanding redemption values have disappeared in many locations. I bought close to 2 million points annually in the last couple years (whatever I could get my hands on) and got amazing redemption values, but this may be coming to an end. There are still a number of locations where it's possible to have 1cpp+ redemptions, but a good part of that is due to the Chase 4th night free and 10% points back offers. For people who don't have access to these cards, it's a lot less compelling to buy/redeem points these days, unless you can find one of the rare glitches that still happen on occasion (for instance, in recent months I booked Tiara Miramar at 34k points vs €650 and Kimpton HK at 21k points vs HKD2400 for 2026 stays).
• The confirmed suite upgrade certs are hard to redeem and in many cases book into rooms I'd get anyway as a Diamond. They now work with most rates (a plus), but the process is cumbersome and staff are poorly trained or there are problems with the system. I'd like to see a way to apply these in the app.
• IHG's fooprint is still lacking when it comes to good ICs, Regents, Kimptons, Vignette, the occasional above-average voco or CP. Hyatt is similar, they have about 50 hotels in the world I like to stay at, IHG maybe 100. That covers 90% of the locations I travel to, and for the rest I rely on my lifetime Bonvoy status.

On balance, I'd be more than happy with IHG for the next three years if they keep the program going without enhancements, and refrain from further devaluing points.