This game is very fun
but it isn't hard. it's very fun and i'm about to finish it 6 more times to unlock the relics. the AI is awesome, very intuitive, zombies follow you or keep moving very long distances.. it makes it realistic, and not like they just 'spawning' zombies around. it actually has very good gameplay and realistic. You have to have good reflexes and level headed-ness, no matter how careful you are you will get shocked every now and then :P
It isn't just a hack and slash zombie game. Literally you have to know and evaluate situations where it's wiser or smarter to avoid certain confrontations.
I haven't had much fun in a FPS game since long.
The game also has great physics, all the movements are very realistic. as like a real person would move, jump and run. Must try this game.
Replayability, LOTS!.
Theres many ways you can choose to head to. I have just finished it once, but since there are relics to be unlocked, I can choose different ways and different cpu partners.
The zombies fights are NEVER the same, it all varies each time you play.
Have only finished it once, so far.