Guns N Roses is metal? I guess leather pants, no shirt, and a can of Aqua Net were the only requirements to be classified as a metal band... A couple of songs that are my favorites that (suprisingly) haven't been mentioned are Master of Puppets and For Whom the Bell Tolls. I've always gone by the rule that if the song is under six minutes long, it's not a real metal song.
How exactly would you categorize them? I'd consider their first 4 albums definitely metal or at the very least a branch of metal.