We went last August to
Legoland and used the waterpark as it was soooo hot that day! lol
It was OK. My boys were 7 and 9 at the time. There was a large, multilevel structure with spray shooters and a giant bucket that dumped water ever 10 minutes or so.
There is a wave pool - but no waves the day we were there
There was a lazy river with tubes that you could build on with foam legos - my boys would have done this all day as they were trying to knock over each other's tube "fort".
There are some slides but there were thunderstorms in the area that day so they weren't open.
One word of warning - we decided to have lunch at the place in the waterpark area - I have never seen a slower operation. There were 2 people in front of me ordering and it literally took 45 minutes to get a couple hamburgers.
Overall, it was a good place to cool off and the kids enjoyed it but I probably wouldn't pay extra for it again.