There are many state campgrounds in the Adirondacks.
Lake George RV park is pricey but very highly rated and regarded—I've never stayed there myself. There are others in the area, too.
IMHO Six Flags Great Escape is unexceptional; it's not a bad amusement park, but Six Flags has bit by bit removed a good bit of what made the pre-six-flags Great Escape neat (and, to be fair, added a bunch of rides and Six Flags stuff). Admission and parking seem to me rather steep for what the park offers.
Just across the lake, Burlington's North Beach park has a pretty nice campground that's reasonably priced, as well as a lovely beach. (This is a city park.)