In 2006 our girls spent a couple of hours there. At the time they were 4 and 10, and when we looked at it on the website they were both gung ho to try it. We booked in advance through Disney dining.
The 4 year old had a great time.....the 10 year old looked crestfallen the second she saw the place, and was positively beaming when DH and I cut our evening short to go get them. My 10 yo played some video games, but it really felt like the place, while very nice, was geared toward younger kids.
When we booked our 2007 trip, the first thing DD#1 asked was, "We don't have to go back to the Sandcastle Club, do we?"