As someone who is alternating between playing this and Assassin's Creed 2, a beautiful game, I think this game looks great. Blowing zombies to bits looks fantastic, and the lighting is really something special too. It's not perfect, I'd rate it an 8/10 in that category...but a 6? No way, don't be pissy. It's made even more impressive by the amount zombies on screen at once...being blown apart. The source engine is the only engine I've ever seen that's able to not necessarily be technologically, "up to par," and yet still have a realistic looking game, IMO it's much better than Unreal 3.
It's funny, people said the graphics in Borderlands were bad too LOL.