A friend of mine was going to a conference at 4 Seasons, and we picked TheHotel b/c it was basically the same price for a suite here vs a room at 4 Seasons (which is within Mandalay Bay). I had read the reviews here and new what to expect.
Check in was painless and quite quick. We got to our room on the 20th floor and as it didn't face the strip, I didn't spend much time staring out at the airport and distant mountains. As has been previously stated, rooms are DARK. Black furniture, dark brown carpets and walls and lights with what seemed to be 20watt bulbs. Energy savings for TheHotel ?
The suite was spacious enough with a full living room and 1.5 bathrooms. The main bathroom might even be too big. The bed was comfortable and the bedding was clean. There was a nice plasma or LCD in the living room, the bedroom and even the bathroom. No coffeemaker though. I find that to be ridiculous.
I also hate to be nickled and dimed, like $20pp per day to use the gym and $15/day for internet.
A number of restaurants are on site. Most are on the pricey end ie $30 for a sushi roll. There was also a restaurant on the top floor, where two appetizers, a martini and a glass of wine ran us $85. The food was great though.
We partied up on theMix on the 62nd floor and there is a great view, but loud. There was also a better(IMO) club on the main casino floor. Great dancing and music and hot women.
I did not use the pools due to the weather, but it looked awesome with the beach entrance and wave machine.
If you want to go to other hotels and casinos and clubs, past the luxor next door, its definitely a hike. We did walk all the way down to Bellagio to check out some of the hotels on the way. This was probably 2-3 miles so certainly not for every one. We did take a cab back though.
All in all I think I would recommend this hotel with some reservations.

This hotel was beautiful and the suites were great. It was a bit of a walk to get anywhere - you had to walk through the whole casino to get to the pool area, but overall amazing and totally worth it! Much prettier than most of the other hotels I saw. LOVE the pool / beach - especially the lazy river!

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.