Personally I think this game is better than Left 4 Dead, and absolutely succeeded in creating a modern reimagining of that classic formula. I understand people being disappointed that there was no campaign versus mode, but as someone who is all about the co-op, this game really delivers. The shooting feels satisfying, and the various mutations and difficulty modes give fantastic replay value that helps make each playthrough feel very distinct. Also, I love how you tilt your gun when crouched, that's the true innovation. Impractical, maybe, but it sure is cool.