I'm actually not as huge into metal as I tend to let on. Mainly prog metal, going into progressive death. I also like 80s thrash, Black Sabbath (whatever they are), and the New Wave of British whatever Metal. Although metalcore can be very good if it's on the melodic side as well. Oh, and fusion metal is fucking awesome, or any metal with jazz influence. It's like peanut butter and chocolate.
My main problem with the more extreme metals is the constant pounding of the bass drum with 16th notes for 3 fucking minutes straight. It hurts my ears. Really bad. I can stand it in short bursts, but not for entire songs! Notice I said 80s thrash and not thrash in general, because thrash nowadays tends to be just that. Screaming can get over-the-top as well, but if it's not too bad, I'll deal with it.
By the way, as a side note, what's with the really short albums? I was looking into Born of Osiris and The Faceless because they were Death metal bands that I thought were good, but the albums were about 35 minutes long. What the hell? Looking at Massive Aggressive (Municipal Waste) right now, that album is 28:49! Carving Desert Canyons (Scale the Summit) was only 40 minutes long, but I thoroughly enjoyed all 40 minutes. That's not so with these guys. I'm not condoning piracy, but asking people to pay up $10 for 30-35 minutes of entertainment won't cut it unless the album is groundbreaking. Maybe I'm too used to my apparently extravagant hour long albums... [/metal related rant]