This is not about Sultan City, but if you are thinking of going to the Grand Ucel Hotel waterpark in Ovacik, please be careful. We stayed there a couple of years ago and whilst it's great fun for the kids, the area around the slides is marble or similar and when wet is extremely slippery. The natural inclination of kids in such areas is to run, and I saw a few people's feet go from under them several times even when they were just walking.
One nasty incident that I didn't see was a teenager who slipped and hit the marble head first a feet feet behind me. When I say I didn't see it, I felt it - and just the noise of the impact sickened me. Poor lad didn't know what day of the week it was. I urged the parents to go to hospital, but he seemed to be a bit better a couple of hours later.
The, erm..."relaxed" Turkish attitude to Health and Safety I suppose provides some of the charm of the country, but it does mean you should take extra care in such places.