I had a quick overnight stay at Muse Bangkok Langsuan (MGallery) to try this property.  It seems the hotel received some criticism in the past due to weak Platinum treatment but it seems this has been rectified.  Based on my stay the hotel does well in various ways and the weakness for me was more about the dark room and the dark theme in the hotel which can be a matter of personal taste.  

Room

I booked the entry level room and I proactively received an upgrade as Accor Diamond to a Duplex Suite.  There was a convenient half bathroom on the lower level along with the spacious living and dining area which thankfully had light-colored floor tiles to offset the dark furniture and the limited window frontage which left to be desired even though it was a room in the corner of the building.  The mini-bar had free soft drinks and they also serve a snack platter every day which had sandwiches, peanuts, olives, and sweets.  

The bedroom and master bathroom were upstairs with good quality hardwood floor but it was black and there again the windows were fairly small.  The master bathroom was fine but the tub was oversized and took too much space.  The bathroom amenities were Shanghai Tang which is appropriate for an upscale hotel brand; the problem is that the soap was missing from the half bathroom downstairs, in fact there was not even a soap holder so it seemed to be by design rather than an omission.  Housekeeping also forgot to remove an old used up soap in the shower.  Those issues are all minor but the water temperature in the shower took forever to warm up which was more problematic and the air conditioning temperature control box kept on making a ticking noise during the night because it was swapping automatically between low and medium speed without us touching anything.   

Overall I find it difficult to complain about the room when receiving a suite upgrade but if I compare the top Accor hotels in Bangkok I saw a non-negligible dropoff between the suites at Sofitel Sukhumvit, Sofitel SO, and Banyan Tree, relative to Muse.

Dining

One nice feature of the Platinum breakfast at Muse is that it was possible to have it as room service whereas many hotels require breakfast to be in the restaurant only.  The menu was very limited however so for a long stay it would have been repetitive.  

This hotel does not have a lounge but they provide happy hour on the rooftop bar for guests Platinum and above from 4:30pm to 6:30pm.  The venue was very nice and I am glad they do not exclude it from happy hour, unlike for example Banyan Tree which does not allow Accor welcome drinks to be in their famous bar.  The happy hour drinks menu at Muse was also reasonably good including cocktails rather than only beer and wine.  The snacks were more forgettable but because this is not a lounge I thought it was fair to serve bar food.

Service

Service during our brief stay was good including the staff proactively calling our next hotel to make sure our room was ready.  They also tried unsuccessfully to redeem Accor points to settle my bill and they contacted Accor customer service who never responded before I checked out, but at least they tried and kept me informed of their attempts.

Gym and Pool

The gym was ok but a bit small.  The pool was on the same floor (19th) as the gym with good city views.  

Wifi

Wifi worked well with speeds of about 20 Mbps.

Overall

Overall the hotel ticks most boxes for a pleasant stay: suite upgrade with 1.5 bath and no carpet, decent quality construction, good service, free breakfast, happy hour in a nice bar for Platinum and Diamond guests, etc.  Yet there were a few hardware issues that would need to be fixed plus the overall darkness was not to my liking even including at reception which was very dark, all of which limits my enthusiasm for this property.