I recently stayed at the MO BKK on a Staycation rate for 17,500THB which is about the most one can pay for a hotel room in Thailand at the moment, but came with 50% credit which I used towards a dinner at Le Normandie. I am a relatively frequent visitor to the MO for F&B (most recently to try the new Kinu by Takagi behind Lord Jim's) so this was about experiencing the legendary guest service for me.
Being alone, I booked an entry level room and that's exactly what I got. It was relatively spacious, though the bathroom was notably smaller than one would get in a new build luxury hotel of its caliber nowadays. The refurb was high quality as you'd expect, and I liked little touches like the metal mini toiletries and the various goodies which were waiting for me (potentially as part of the staycation rate). At the MO's price point, you are clearly paying primarily for the service and not the room though - it doesn't compare to the Siam or Waldorf Astoria rooms, though in those I haven't seen the entry level rooms as other hotels appear to be much more generous with upgrades at the moment.
Service was classical and highly polished. I can see how the hotel has built its reputation on it. For me personally I found it a touch cold (with the exception of reception, who were lovely) and wasn't a fan of the way staff members would often about turn and run away if I entered the corridor or the way they had a habit of lurking around corners (e.g. by the pool) to keep an eye on me without being fully seen - while offering excellent service, of course. What I noticed most was the sheer number of staff, more than any other hotel I can remember seeing recently. The middle level management were also highly visible, including someone who greeted me by name as I walked out of the elevator in the morning apparently by my demographics of being a single white man alone.
F&B is obviously legendary here. The Bamboo Bar is always special and I enjoyed the chance to try Le Normandie including their signature uni and caviar which matched with the right wine was rather special. Whenever I am in Bangkok I expect I will be returning to eat or drink here, but I didn't feel the hotel overall is a great fit for my personal preferences. At the absolute top end of the Bangkok hotel market, I feel more comfortable at the Siam which to me personally just feels much more welcoming and where you get a true stunner of a room at twice the size.