I visited the spa at TheHotel after receiving a spa credit from making the hotel reservation through American Express. It was an excellent experience.
After being greeted upon entering, a spa attendant showed me around the amenities in the spa included with the services. I took advantage of the wet and dry saunas, and they were pretty awesome. The attendant even came into the dry sauna and offered cold drinks and a cold towel. That was an awesome touch.
The massage I had was excellent. The actual room was calm and peaceful, but the music playing overhead was a bit strange. Show tunes a la Musak, not very relaxing, at least to me. I also had a manicure, which was excellent.
Overall I would definitely return to the spa. It was well appointed, immaculately clean, and the customer service was top notch. It was a little pricey but everything Las Vegas is, so it was in line with expectations.