Who are you going with? If it's with your g/f / spouse, then I heard it is reallllly nice. Plus, you can go to the other "Palaces" there...Cancun Palace, Beach Palace...
We have been to almost all of the resorts. The Moon is great, the only problem is how huge it really is. Plus the beach/ocean are has some issues with seagrass, which makes it close to impossible to go into the water.
It is a great resort and if you are thinking spring break or something should be great.
If you dont care about being in Cancun, go up to Playa Del Carmen area and stay at the Aventura Palace. It is adults only (no kids at all) and is a lot of fun.
We have been to:
Moon Palace
Aventura Palace
Xpu - Ha Palace
Spa Palace - - This place is kick ass, but they are letting kids in
and many others.
Let me know if you have any specific questions and I am sure that I can answer them.
We stayed at the Gran Caribe as well. Kicked ASS!! Marble floors and shit. My best friend honeymooned at Moon Palace and looking at the pics it was just as nice, if not more so than Real.
We stayed at the Moon Palace 2 yrs ago..... It was awesome. Nightlife sucked but it isnt that big a deal to go into town. The club @ Moon Palace got pretty wild. Do yourself a favor and take the dinner cruise.