Not as bad as people say, but not good either.
The main problem with Cool World is that it isn't funny. The animation is chaotic and energetic, but it translates to a lot of insignificant sound and fury. Human wise, everyone is lost: A very young and wooden Brad Pitt stars as the human detective of the toonverse, Gabriel Bryne is non-presense as a comic book artist, and Kim Bassinger is attractive, but dull as toon-turned-human Holly Wood. The idea of it being illegal to have a human copulate with a toon is potent stuff, but it only gets a superficial treatment. Ralph Bakshi is a fine animator and a piss poor live action filmmaker. You can see the money on screen, and its fun to watch, but unsuccessful. Sometimes you don't even know if some things are supposed to be funny or just cheap, like the live action backdrops of the toonverse that looked like they escaped from a a community theater abstract set design closet.
The original pitch of Cool World being a horror film about the offspring of a human and a toon would have been better material - like the original DARK HORSE inception of THE MASK.