Out of hardcore evolved metal, and out of metal evolved metalcore. Metalcore is obviously metal influenced and because they're of this there is more complexity in the writings of guitar, more noted riffs added to it than hardcore has. Some say that it has punk influences, but that depends on what band you are talking about. There definately has to be screaming in any form of metalcore which is the low pitched growling. It has a lot of breakdowns, most of which have the "JUN JUN JUN" sound with some double bass. Metalcore was a lot better a couple years ago before more and more band's started learning that you can tune into drop-C, use only thin picks, and get a drummer who knows his double bass to become a metalcore band.

I don't really know to much about it. End.

Metalcore Reccommendations (with albums):

Converge - My favorite album of theirs is Jane Doe, although anything you get by this band will be awesome. They are one of the most influential metalcore bands of all time and rightly deserve it.
Unearth - The Oncoming Storm
Poison the Well - The Opposite of December (One of my favorite metalcore bands.)
As I Lay Dying - Frail Words Collapse
Death By Stereo - Into the Valley of Death
Every Time I Die - Hot Damn!
Norma Jean - Bless the Martyr and Kiss The Child
Misery Signals - Of Malice and The Magnum Heart
Darkest Hour - Hidden Hands of a Sadist Nation
Throwdown - Haymaker
Fordirelifesake - Breathing In Is Only Half The Function
The Agony Scene - The Agony Scene
Cave In - Until Your Heart Stops (Don't get anything else by this band, they recently switched to an alternative style and its horrible.)
Walls of Jericho - All Hail The Dead