As long as you're not going into this expecting "western" style levels of luxury, you will not be disappointed.
You will, however, be entranced from the first moment you glimpse the island from the road. It's an amazing experience to walk through the door marked "Taprobane Island (Private)" and get used to the fact that you are currently (temporarily) in possession of your very own private island.
The staff were fantastic and went out of their way to make our experience magical, and the food was consistently spectacular (go for the Sri Lankan options - if you order western style food in Sri Lanka and find it disappointing, that's your own fault).
There is no air conditioning, but it wouldn't work anyway, as the buildings are all quite open to the sea breezes. The sound of the waves crashing against the rocks is soothing (and to be expected - you're on a small island after all).
The beach is fine to swim in if you want to be gawked at by locals, but why would you want to when you have your own infinity pool overlooking the Indian Ocean?
You will get wet walking to and from the island through the surf. If you don't want to brave it the local fisherman will ferry you back and forth for a fairly extortionate fee, but it's just kind of all part of the fun.
Great open communal areas to play cards with the family, plenty of island to explore - still regretting we didn't quite get around to playing hide & seek.