We went a couple of years ago. I agree with everyone who said two days tops. There just isn't *that* much to do.
One night (which as PPs said includes 1.5 days in the water park) is plenty. You will be practically deaf from the roar of the water by then. We got there right at 1 PM on the first day, did the water park until evening story time, then the full day the next day including the story hour.
DS age 9