Being a big fan of zombie games, I was a little disappointed by this. Mostly because I had bought the game with intent on playing coop mode with a friend of mine, but then discovered that only about 4 of the 20 levels were playable in coop mode. Plus it's only an endless onslought of zombies, no real goal besides surviving as long as you can. What's the point? I'm going to die eventually anyway right?
Anyway this game is played with a skyview pov, or almost third person if you zoom in to the max (but I can't see much when it's like that, so it's skyview for me). Use of the WASD keys is for moving around, and mouse to aim and shoot. a couple other various buttons for locking/unlocking weapons, jump-rolling, spending skill points, etc..
The singleplayer aspect of the game was very amusing, however. Playing through the levels was fun, seeing as they actually ended (it also has a progress bar at the top of each level indicating how far you are for that particular level). Plus after each level you get a chance to replay it, giving you an extra star for beating it. This can be done up to 15 times (I think). After that you can still replay them, but it won't change the number of stars you've gotten for beating the certain level.
The first levels are quite easy, but after a bit some harder "Boss" zombies get added. For example, the Minigun Zombie, The Butcher, Chainsaw Zombie, etc..
You start off with a pistol and a melee weapon. But killing zombies often drop different, better guns. I loved the fact that there were so many different weapons in the game (about 70 or so including melee weapons). Killing zombies also sometimes drops powerups, giving you aid in your fight against the horde.
There is also an rpg aspect included in the game. (the only sad part being your level restarts every round, so you don't keep your bonuses past the current round you're playing) The way it works is that based on every kill you gain a certain amount of experience. After a while you level up and can spend your points in certain skills. Some skills are affected by the powerups you can pickup, and others are just always on (without picking up a powerup)
ending with a bit of gameplay from yours truly;