Black metal is generally less heavy, not downtuned, faster, involving much more straightforward rhythms, and having actual harmonies. Also, vocals are pretty different - rasping rather than growling. Personally, I like both, though as with many genres there's a huge load of shit to sift through to find the good stuff. I like Emperor, Bodom (not entirely black metal), Shade Empire, Immortal, Old Man's Child, and a bit of Borknagar. Other stuff that I found was just annoying, and being as it's the latest trend, there's a LOT of other stuff. Either way, there is no arguing that the whole black metal bit that isn't the music is the funniest shit around - between the corpsepaint, and the paganism, and the weapons, and the nordic heritage, and the arson...