We went there on our honeymoon in 9/95. Stayed at the Omni on the all-inclusive plan. Not sure if it's still like this, but when we went, you could stay there either all-inclusive or not. The all-inclusive was a great deal, and I'm glad we chose it.
And we chose the Omni largely because we wanted to try an all-inclusive, but were concerned that if the food and drinks were awful, our honeymoon would be ruined. We figured the Omni was selling the same food as they were giving with the all-inclusive, so how bad could it be? We needn't have worried; the food was wonderful and so were the activities included in the deal.
Our room was spectacular. Gigantic bed and bathtub. Marble walls and floors. A stone balcony covered with flowering vines that looked out over the Caribbean Sea.
One of these days, we're going back to Cancun with our son, and I think we'd like to try the family Palace. There is a number of "Palaces" e.g., the Moon Palace, the Sun Palace, the Cancun Palace, etc. Can't remember which Palace is geared to families, but that's the one we'll pick.
There is one Palace specifically for couples. Try a 'net search on "Moon Palace" and you'll find it.
Xcaret was our favorite day trip while we were there. It's a natural water park. Its lazy river ride flows through real caves. Awesome!