Coming from a metalhead and hardcore background, I can easily say most metalcore sucks, especially the further fusing of subgenres, like deathcore. Bands like BMTH are abysmal where the entire emphasis is being loud, heavy, fast/slow/fast/slow, and fun, just like whatever pop rock garbage comes through the radio, just a more radical facade. The worst part is (and I know people like this) these guys who think they're into "death metal" because they downloaded a few BMTH songs, while never even having heard of a Massacra or a Demilich or what have you, and also thinking that At the Gates' only album is Slaughter of the Soul.
However, Integrity, being the first metalcore band and, really, the only one who got it right, is worthy listening, notably "Seasons in the Size of Days", "Systems Overload", and "Humanity is the Devil". They somehow managed to balance hardcore punk with extreme metal without the two losing their efficacy.