Who Framed Roger Rabbit is pretty amazing. Blending live action with cartoons had been done before, but never quite this well.
Apart from the technological achievements, I think this movie is also pretty clever. Playing up the film noir and giving a wink to the history of cartoons, the plot, characters, and concept are original and often very adult.
This is one of my favorite movies from the 1980s. If you haven't yet seen it, you should give it a try.