Now, last night I finally got around to watching 'A Scanner Darkly' - a movie based on a Philip K Dick novel with Keanu Reeves and Robert Downey Junior that was done in a cartoony style. Overall it was quite good, although I don't think I'd go out of my way to watch it again. It seemed to meander around for the majority of the film with not much in the way of plot driving it forward - the only thing that saved it from the off button was the rather excellent banter between the three lead characters - particularly Downey, who was superb - although he mumbled a lot! Then it picked up with the last quarter with a couple of twists.
I'm not sure what the benefit of the cartoon style was. It would have been just as good a movie if they'd filmed it in a traditional style. At first I assumed that they'd done it to keep costs down - you can get away with ropey lighting, dodgy sets and even crappier acting if you're cartoonizing them. This theory only stood up if the cartooning process was some sort of cheap automated one, though.
Turns out they hand-drew each frame on top of the filmed frame and it took about 50 people 18 months to complete. So overall the costs would have been about the same. So the only reason for the style was to...er... make it look a bit different from other movies and maybe draw in a few curious punters to a movie that probably wouldn't attract that many viewers. I don't think it added anything, although it was kinda pretty.