Denver is about as good as it gets right now. Everything has flushed with the rain so this is the cleanest year. Having said that, I'd go to Golden PP or Lyons. Lyons is crawling with boaters and is a fun time. The Shellys section of NSV is a good class II/III.
*edit* What I mean above is that this is as good as the Denver play park gets. Later in the summer is when the bacteria load explodes.
On the river, I can abandon who I am and what I've done. However brief it lasts, while on the river I am nothing important and everything insignificant. I am flotsam, and happy to be so.