Well, I only played campaign so the glitches I saw came from there. And almost all had to do with the NPCs not following orders, not following Marcus, just running around aimlessly and refusing to fight, or running at an enemy only to die without doing a thing despite orders.
The only other glitches involved me glitching up onto things on accident and not being able to move and having to restart a level. Usually only minor annoyances, but eh.
The difficulty factor was nice though. I played once on Casual because I wasnt sure if it’d be harder than the 360 version. It wasnt. Then bumped it up to hardcore, which proved a nice challenge, especially since I’d never played hardcore alone. Only co-op.