I've hiked almost half the trails in the park. The Sky Line trail is my favorite. It's a very beautiful place.
I like to visit during the "off season".... Since I've lived in both Seattle and Portland, I don't mind the rain. I remember the "T" shirt from my Seattle days: "Seattle Rain Festival, September-May" and a friend was fond on saying: "if summer falls on a Sunday, we'll have a picnic".