Pros:

Imaginative environments, rich in details

Many alternate routes, alternate events

Custom voice acting

Custom melee, whack the crap out of the undead with their own body parts!

Cons:

Low fps in certain parts. For myself, the worst part in the whole game in on map 3 (I think), when you drop from a hole in the floor to a smallish flooded lab. 

Strange bug at the onset of map 3 where I see blue artifacts flickering around me.

Conclusion:

Superlative campaign, way up there with Suicide Blitz 2 and Back to School.