Couple things about your Aqua Fun Add-on:
1. It's pretty awesome
2. You need some bikes up at the top of the slides (going down the tubes in first person on a bike is super disorientating haha).
3. You also need some cars up there (the Comet is perfect because if you flip it it'll just roll back over, also it drives upside-down on the top of the tubes very nicely).
4. There needs to be a road going up there, perhaps a nice bendy road with lots of hairpins?
Other parts of your mod:
1. I was thinking that putting some boats around the island would be nice.
2. There's still some invisible holes all around the northern most area of the map.
3. On the dirt-rally track it might be better to blend in the edges of it so they're not so rounded, making it easier to get back on the track.
4. The road leading to the dirt track and the buildings is raised up and if you fall off you have to drive back to the main track's pit to get back up.
5. Where the slides and dirt track are there are still some invisible objects.
Anyway I really like your mod, and good luck with future releases.