Except for some very nice special effects, involving heaven, hell, and war, the animation is true to the deliberately clunky "paper cutout method" of the TV show (long since done with computers rather than with real paper cutouts). The characters' legs appear to be sewn tightly together when they walk, and there is no attempt at "visual beauty." In the style's defense, the animators manage to produce an extraordinary range of facial expression with minimal movement -- no small accomplishment in itself. And, most importantly, if the technical work were more sophisticated, the movie wouldn't be nearly as funny -- which is, after all, the whole point.
The one negative aspect of the film may have been a fluke of the press screening: The sound was grating and murky. The painful volume in the theater was no doubt part of the problem. But, even compensating for that, it sounded as though the sound mix was excessively shrill and muddy. In one number where bits of several songs are reprised all at once -- in the manner of the pre-rumble sequence in West Side Story -- the parts fused into an unintelligible whole, an ugly bouillabaisse of noise. I'm sure it would have been much funnier otherwise.
Still, for South Park fans and for those without priggish sensitivity to the way their children really talk behind their backs, Bigger, Longer & Uncut delivers: It's never less than funny, and at its best, it's truly hysterical.