I haven't been to SandCastle in years, so I can't comment on some of their newer attractions, but when I was there it was really fun. There are tons of slides, ranging from the fairly tame to the really intimidating. There is even one that drops off partway down, so you fall into a deep pool of water. Another has several stops along the way in elevated pools, so you have a little pause before going down the next part of the slide (there are lifeguards in each pool to keep you safe).
There is also a Lazy River for those who want to just float and relax, hot-tubs (including the world's largest!), swimming pools, go-carts, a boardwalk (with food, arcades, and gift shops), and more stuff they have added since I was there last (a big wave pool, among other things).
At night, stay around for the nightclub (one for over-21's and one for under-21's, although I think the latter is open only certain nights).
There is even a place to dock your boat on the river, so anyone out for a cruise on their motorboat or yacht can stop by.

Recommended: Yes