The guns have a very good feel to them. They manage to completely convey the power of the gun in a nice cinematic way, and don't jerk your view around unless it's from a powerful shot (god, I just got WaW and the trenchgun's view-jerk from the pump action makes me want to bomb Treyarch) As Jigglebelly said, the feeling of the "ironsights" with dual pistols feels kinda intense, even if it doesn't help your aim enormously.
The levels are all pretty unique and interesting, with different color palettes.
I kinda like that the zombies are slow. If they were fast, they'd need to die easily to be balanced (L4D) which reduces the glamour of an enormous horde moving towards you.
Finally, the Patriarch. It has been SO long since I've seen a boss enemy in an FPS that was really engaging, complete with boss music and special attacks you need to memorize. Added to that, the fact that you're beating him as a team, it's just unlike anything else. (L4D tank: Okai guyz plan is SHOT HIM.)