For the price it is on Steam currently it would be a sin not to get this game.
The game itself can seem repetetive at times, but the aim is to level up your class to become better with certain weapons, for example the sharpshooter class gives you extra pistol damage and less pistol recoil, and with every class level you increase the damage will increase by 5-10% and the recoil will decrease significantly too.
There are eight classes in total which are Sharpshooter, Commando, Support Specialist, Medic, Firebug, Beserker and Demolitions. Each class provides different class perks.
The look and feel of the game is very impressive, the graphics are smooth and dark to portray the zombie apocalypse style gameplay better. Like Left 4 Dead it has a film grain type clarity to it, which enhances the feel of the game.
There are also plenty of maps in the game to keep you engrossed for longer, each map has plenty of different areas to hole yourself up in for protection, but you have to stay with your team mates otherwise it will get a bit to hairy to handle for you alone (unless you have a high level class or an expensive weapon). On each map there are a series of waves of zombies which end after every member of that wave is killed, when this happens you hear the shopkeeper say that the shop will open back up (the shopkeepers voice is SO annoying).
This is a nice cheap game that is easy and enjoyable to play, especially at a LAN party with your friends.