[MetalMilitia]

Top 10 things which make L4D rock:
1. Zombie physics/animation blending.
2. A.I. Director.
3. Accurate, powerful weapons.
4. Dynamic music.
5. Mechanics to encourage team play (smokers/hunters will almost certainly take down anyone that goes rouge).
6. Automatic voice commands ("Weapons here!")
7. The way pipe bombs attract zombies.
8. Tank battles.
9. Perfect melee combat.
10. Level design.