It's a simple, funny movie with crude humor and some hidden social commentary. The art style is well done, and the humor is just witty enough that most of it doesn't induce too much cringe.
It takes a sharp dig at religion, which comes across as somewhat heavy handed, and essentially serves to paint anyone with unfounded religious beliefs as ignorant fools. The main character essentially finds evidence that the "gods" and afterlife are fake and then has the burden of proving it to the ignorant masses. The flip side of this coin, however, is the lesson of how dangerous blind faith can be, and how belief in something unproven can motivate people to be needlessly violent, arrogant, and judgemental. In all, it could have been handled a little more delicately than it was, but it's obvious that the creator was trying to get a message across in that regard, and no true art (yes, all movies are art, even the immature, crude ones) survives without at least some residue of subjectivity.