Great game it's very fun and exciting! Couple of problems me and my friends had on one level( spoiler alert). But the level when you had to defend the chains for the elevator. Couple bugs and glitches that made the level way too difficult.
We were getting shot through walls, couldn't pick up guns or med kits and we think an ammo crate just disappeared. We thought maybe because we're on the hardest difficulty, no same problem on normal. It was very frustrating because we want to beat the game on the hardest difficulty but the bugs and glitches were too challenging for us on the level.