I've stayed there once, after having walked through the prior year while staying at the (now) Wyndham Crystal Palace.
Atlantis is a beautiful hotel. The rooms are very nice, the service quite good, though of course not Disney level, but what is?
As much as I enjoyed the beach, the pools, the casino, aquarium, etc, I must say it was one of the few vacations I've ever taken where I was literally lounging in the pool and mentally calculating how much it was costing me per minute to be there.
If you stay on-property for meals, the restaurants are ok, but the prices are truly outrageous. A beachside burger and fries was around $12, a bottle of water about $5. A steak at one of the fine dining restaurants was around $60. This was a few years ago, it could be different now, but I doubt prices have decreased!
When I go to a resort like that, I like to just relax, not scrounge around trying to find the best deal on breakfast ( I do that all all year to save for my Disney trips). that being said, it was hard to enjoy the breakfast buffet at about $16 each.
Maybe I'm just cheap! If money is no object, go for it.