It's sometimes actually funny, sometimes actually moving, and it seems to be in favor of increased gun control in the U.S. (which I'm in favor of myself), but it should primarily be viewed as entertainment, not as a representation of actual reality.

See:

Spinsanity's coverage of the film

and...

The Truth About Bowling for Columbine

Moore responds (sort of) on his own site:

How to Deal with the Lies and the Lying Liars When They Lie about "Bowling for Columbine"

Though he frontloads this with a bunch of unrelated crap, and ad hominem attacks before he actually gets to "the facts".