MORE SPOILERS
The final stages of the film are kind of a misfire in a couple ways. I didn't need to see the giant santa (in fact, I never actually expected to see it), but I did expect that we'd reached Stage 2 of the film, not the beginning of the climax. It was indeed too short. Although, I find it hard to complain about a movie being too short, considering how much worse it is when a movie is too long. With its silly ending the film is a bit of a trifle, but it is an extremely fun trifle.
I think younger people will really dig this film. I can easily see it having been one of my favs back when I was 12 or so.