Any cartoon from the 80's/90's that has since become a CG movie ruins my childhood. Possible exception: TMNT. But Garfield, Scooby-Doo (not an 80's cartoon, but aired a lot around then), Alvin and the Chipmunks, Smurfs... fucking stop it!
Want legitimately GOOD movie versions of some of these properties?
Garfield: any of the old TV specials
The Chipmunk Adventure - Still one of the best 80's cartoon movies. The music, the villains and the action scenes are awesome.
I swear, if they make a Peanuts CG movie I'll kill somebody.