For starters it's unlike any other vampire movie, at least that I've ever seen. It's a vampire romance for sure, but at that age the love is of a more innocent kind, whereas other movies have an undertone of lust in the violence. The relationship is more awkward and furtive than most you'll see. There is a detached feeling in the film, mostly because the two characters are very isolated, either by their nature or by their environment.
The violence is another interesting part of the movie, as the adults are horrified by the blood and death, but most of the characters are children and they seem to move unaffected by it. The physical violence at least. The psychological effects of the intimidation and isolation that Oskar is put through obviously affect him. But when Eli uses violence to protect him from those things, he doesn't see the violence but the intent behind it.
The movie just has a lot more depth and substance than most "genre" films. But if you need a faster pace, more exposition, etc. then I can understand why the film might not suit some people. Or some people need explosions and a bumping rock soundtrack, whatever floats your boat.
They say you should never hit a man with a closed fist, but it is, on occasion, hilarious.