At it's very heart is Quentin Tarantino's take on a Hong Kong action flick. The story is told with such zealous childish glee that you can't help but find it endearing despite the incredibly graphic violence and gore. It's a parody of almost every Hong Kong Kung-Fu movie I've ever seen and them some. There are also some very distinct anime elements to it as well.
I couldn't stop laughing the whole time because even when the movie wasn't try to be funny, it was funny anyway because of the ridiculously excessive blood and gore. The characters themselves only add to the "festive" atmosphere and are so extreme that they become cartoon-like and two-dimensional, which in this case is a good thing.
Anyways, very cool movie. Just go see it because it's really pointless for me to sit here and expound the sheer AWESOMENESS of it.
Another really AWESOME movie is Battle Royale. I'll save that for another day. If you're curious and want to see it (maybe because Chiaki Kuriyama (Gogo) is in it), make sure you won't need a good night's rest that particular day. Seriously, it's totally crazy-go-nuts.