I stayed here for four nights. The service was top-notch and friendly. The rooms were very nice, with a couch and chairs in the living room area, two very comfortable beds, and large bathrooms. Each room had a large flat screen TV, and even the bathroom had one. The decor is very modern, which is not my taste, but I didn't really care.
All that being said, I'm not sure if I would stay here again because of the price. It was fun for a bachelor party weekend, and the suite was handy for watching sports while pre-gaming, but Mandalay is a little out of the way. There were definitely other options that would have served the same purpose for a lot less money.

THE Hotel is truly fabulous - the rooms are spacious and comfortable with separate living area so that if you're there on business as I was, you don't have to live/sleep/eat/work all in the same room. Huge bathroom - just what you need to feel pampered.
My only critcism is room service - usually food orders took the full 45 mins to arrive, and when they did the food was not piping hot. In addition there are one or two truly awful items on the menu - the chicken wings sounded great on the menu but turned out to be deep fried in a dark batter several times over - I suspect they were a few days old - I have eaten better chicken in KFC! So be wary about what you order from room service, the better option would be to go to one of the many restaurants in the Mandalay Bay hotel down the corridor and get take out - most of them will let you charge it to your room.
That is my only complaint though - I would definitely stay there again.

We stayed in a V suite for 3 nights. We were disappointed to only get a sideways view of the Strip, but loved the huge room. The bathroom in particular was enormous with a mammoth bath easily big enough for two and deep enough to drown in. The rooms and public areas of the hotel were calming and exceptionally tasteful. After the madness of the Strip it was a little oasis and lovely to come back to. THEhotel is at the bottom end of the strip (and the tram wasn't running when we were there), but it's not a long walk to the MGM Grand to pick up the monorail. We drove some days and walked some days and didn't find it a great inconvenience. The shark reef is worth a visit too.

Everything about Thehotel at Mandalay Bay was classy. The room was great and we loved the Cafe and the view from Mix is a must see. The spa and gym were amazing and there was an excellent selection of restaurants in the Mandalay complex. The staff was efficient and responsive, but we did have some problems with the maid service (we’d leave at 9am and return at 4pm and the maid was just getting to the room). A big drawback for us was the lack of a coffee maker in the room (a must have for us) and the location at the far end of the Strip. Getting anywhere else along the Strip was either a considerable walk or required a taxi. The tram that serves the three resorts (Mandalay Bay, Luxor and Excalibur) was down during our visit. While we enjoyed our stay at Thehotel, and rate it highly in most categories, we would probably stay somewhere nearer the heart of the strip on our next visit.