The graffiti on the walls, like Portal from the previous year, lets the story drip out in a more organic way. I like the little comments the four characters let drop sometimes; I wish they used it more often. I also like how its told from the perspective of common people, who have no idea what's going on with the military, or other cities, let alone the world. Its the right amount of story to hold things together and not interfere with the non-stop action.
I like the zombies a lot. They are just human enough to creep you out, and inhuman enough that you don't feel bad wiping them out. Its unfortunate they are all the same gray color, but at least they have varied forms of dress and voice. Unlike old fashioned shuffling zombies, these engage in humanistic behaviors, which makes it so much more disturbing when you open fire on them.
I also like how they use the modern secular interpretation of zombies, in that they are infected, not undead. Things are a bit more ambiguous with the witch, but I'm guessing the supernatural music is mostly to cue the player, not an explanation of origin. The specialist undead are mostly silly, but without them it wouldn't be much of a game.
Some things that take you out of the game are the waves of grunts who appear like clockwork every couple of minutes. I like the idea that certain sounds attract them, like car alarms and the beeper on pipe bombs, but your constant gunshots don't.
As much as I would like to meet a few more civilians, I guess it would detract from the 'us four against the world' vibe.
After I finish single player on normal, maybe I'll try a higher difficulty, now or later. I think this game may be in my rotation for a while as something easy to pick up and put down on when I want this kind of play.
