Now a days it's pretty much pedal riffing with EXTREME emphasis on breakdowns, throw in some dissonant breakdowns here and there, chugs plastered throughout the song, clean vocal pop choruses that can be/usually are auto tuned, and a lack of flowing transitions in songs. "Cookie cutter" metal. There is almost 0 hardcore influence in 99% of metalcore, which is another reason why people are turned off by the idea.
Metalcore used to be bands like Coalesce, Earth Crisis, 7 Angels 7 Plagues, Hopesfall, Poison the Well, Converge. Now the bands you'll see as metalcore are As I Lay Dying, Asking Alexandria, Bring Me the Horizon, every other band you'll see mentioned in this forum.
There are some metalcore bands that still give me faith in the scene. Misery Signals, It Prevails, Counterparts, Shai Hulud, all great bands that actually sound like hardcore mixed with metal.
EDIT: ^ Beat me to it.
One thing though. Punk = Soft? I disagree.