My sister recently visited the Senses Spa at the Grand Floridian, and she was in absolute heaven. I can't remember what treatment she had, but she told me that the experience was life changing and that it's the best spa visit she has ever had.
A month prior, she had visited the Senses Spa on the Disney Fantasy (which was her best cruise ship spa experience), but she said that she really didn't understand the theme until she visited at the Grand Floridian. It was a journey through the seven senses, and you do different things throughout the visit to activate a certain sense. This was something that they didn't emphasize on the Fantasy.
Another thing she enjoyed about her Grand Floridian Spa visit was that they didn't try to sell her a product. On the cruise ships, they are always finding things wrong with you and pushing you to buy things. They'll even write you a "prescription" for different products they sell. It can really take away from what's supposed to be a relaxing experience. She was grateful that there was never even a mention of products they had for sell while she was at the GF spa.
I will ask her more about her spa visit later, but one piece of advice that she did give me was that she learned through research beforehand to bring a bathing suit. When you purchase any treatment, you have access to their whirlpools and rainforest relaxation room for the rest of the day. She enjoyed spending extra time after her treatment to enjoy the facilities and was glad that she had brought a swimsuit.