People hate it for not being Left 4 Dead, guess what, it's much better than Left 4 dead. The core gameplay is very solid and fun, every single run feels different from the previous, 150 hours in and I'm not bored one bit, I thoroughly enjoy sherpaing people in nightmare, as well as grinding every ZWAT skins. Now it just needs more content and maybe modding in the future, then this game will be even more legendary than L4D.