Quiet in April but probably not in the summer!
General: There are four campgrounds in Clear Lake State Park: Upper Bayview, Lower Bayview(both of which were closed when we were there in April), Cole Creek, and Kelsey Creek. This review focuses on Kelsey Creek.
Site Quality: The sites all appeared to be level with paved pads. No hookups throughout the park. Not a lot of privacy between the sites but decent separation.
Bathhouse: Clean but as we have found in other California state parks, no soap! Showers take tokens which must be purchased on-site
Activities: Limited hiking on a short nature path. In season, there is boating, swimming, and fishing. It was very quiet when we were there in April but I imagine there would be quite a different vibe come summer when the campground would be full (which is why we like camping in the off-season!)