We have done this twice -- once on Dream and again on Fantasy -- and loved it. Honestly not sure if I would do it again, given the price, but it's fun at least once (or twice, I guess!).
It is a 2.5 hour experience. You go into your respective locker rooms, change into robes, and then go into the "villa," which consists of the massage/treatment room (two massage tables, side by side, but with enough room to walk between them), a bathroom, a huge shower that looks out over the verandah, and then the verandah itself, which has a hot tub and a couple of nice big lounge chairs.
First off is a foot/leg scrub out on the verandah. The two masseuses bring out big copper (?) tubs of hot water, and the two of you sit in chairs with your feet in the tubs while the masseuses sit in front of you and scrub your feet and lower legs (an exfoliating type of scrub). This takes 10 minutes or so, and then they give you about 20 minutes in the hot tub. Depending on the day, it might seem crazy hot out there already to be sitting in a hot tub, but still very nice. You can also use this time to test out the huge shower, especially if you're growing weary of the small bathroom area(s) in your stateroom -- ha!
Then you head back in (after careful knocking on the verandah door by one of the masseuses to maintain some privacy) for your treatments. At some point prior to that, they give you three or four choices of treatments, so by this time, they are ready for you. I have gotten stone massage both times, but there are two or three other choices, including one treatment that DW got the first time that had her wrapped up in foil like a burrito -- a seaweed wrap, maybe? -- she opted against it the second time!). These treatments are something like 80 minutes and seem like they will never end, but in a good way. I actually fell asleep. But yes, to confirm, you and spouse can choose different treatments.
After the treatments, they send you back out on the verandah to the lounge chairs and bring fruit skewers, chocolate-covered strawberries and a variety of hot tea options, and leave you to relax for another 15 minutes or so.
Last but not least...they bring you back into the treatment room, where they have so carefully laid out a few products to recommend to you (each of which is roughly $50 to $60...ouch!). The products are selected based on some questions you might have answered on the pre-treatment questionnaire or during your treatment -- e.g., I mentioned to my masseuse that my job could be stressful, so naturally, there was some de-stresser oil available for purchase. Go figure!
All in all, it is a thoroughly relaxing 2.5 hours...as long as your kids don't call you on the Wave phone while you are on the massage table...trust me, that can suck the relaxing right out of you!