Metal is mostly an instrumental based genre, but vocals range from anywhere between clean singing to deep growling to dramatic tenors to mid-to-high pitched shrieks or any combination of the sort. Black metal tends to be the closest to anything resembling "screaming", but it's not so much screaming as it is just harsh high-pitched vocals.
But like I said, it's an instrumental genre. No matter what the style, the vocals are simply just another instrument to people like me. The aggression within the instrumentation is its main attraction.
Also, in case anyone's interested, I have list of metal album recommendations that I've been passing around, encompassing a variety of subgenres. If anyone's interested, just ask and I'll PM the list.