Challenging game packed with action and zombies (you don't say?).
You will soon be outnumbered/swarmed by pack of undead with hostile intentions, there is quite some tactic involved to survive (and reflexes).
I found it quite difficult even ad the simplest difficulty level (to be expected, this being a KKairos game).

edit: it was pointed to me this is not by KKairos. Well, I guess dMZX people have an insane love for difficulty :P.