The water park is fine, but the theme park is a rip off. Only 4 roller coasters and one was broken when we were there. Carnival games were $3 and up for one "throw of the ball" type games, and the drinks were more expensive than Disneyland.
The park does not offer rain checks for inclement weather so make sure you check the weather. The pools are not really heated, so if it's 55 degrees and raining, you'll freeze. We made the mistake of buying a two-day pass.
Unless it's really hot and you plan to stay in the water park for multiple days, just buy the single day pass. You can do it all in one day and have plenty of time left over to do it again.
Don't bother staying at the RV Park across the street. Their staff is incompetent and does not understand the concept of customer service.
We stayed here in early July of 2010. We made early reservations and intended to end our Yellowstone trip at Silverwood RV Park. Based on my experience with the staff, I will NEVER stay at this park again.