Fun, but can drag on a bit...
This game is a great shooter and has a wide range of weapons that are all effective and fun to use. The bosses can keep you on your toes and make you pay attention to what you're doing. But, it will start to get repetitive somewhere for everybody.
A couple tips: Get up in that zombie's face with the shotgun for maximum effect and save some shells too; Press D to switch to your melee weapon to take out barricades as it will take way too many shots with any weapons to break down; During bosses, juke your way through the normal zombies and try to use your ammo only on the boss; Lastly, the fat zombies explode when killed and take out most other zombies in proximity.
Enjoy!