I haven't played this game on the PC yet, but my friend owns it on the Xbox 360 and I've tried it on there. It plays like a mix between Fallout 3/New Vegas, and Borderlands. The Skill-trees are similar to Borderlands in you have 3 different main trees that branch down, and the quests are much like Borderlands "Run here, kill this, return here" kindof quests. The looting system though is much like Fallout, where you click on the bodies to see what each one has on them, take what you want and leave the rest.
It's not as good as everyone was hyping it to be, but if you're a fan of Action RPG's, and Zombies it's worth a shot. Personally I loved Borderlands, and I love zombies. So, I'll give the game a 7 out of 10.
Not for everyone though.
Next game I'm really waiting for is Rage.