Have you read my review of Left 4 Dead 2 yet?

No speedrun for me! If you can run from A to B without taking much damage, your difficulty level is set too low. My personal difficulty level is that every team member survives in the game. Players who constantly run ahead, use loot themselves or are out of reach when things get tricky are, in my opinion, bad team players, but luckily you have the option to leave the game, which is what I do.

The AI Director is the artificial intelligence behind the game. It keeps an eye on you and reacts to things like your speed or how far apart you are - and it decides when to unleash a horde or special infected on you. Some animations in Left 4 Dead 2 are seen far too rarely. My favorite is:

The tank is attacked by zombies and special infected, sometimes immobilized and, in the best case, beaten to death!

To do this, you throw the boomer bile at the tank when a horde is announced acoustically or there are a lot of zombies hanging around in the area. The advantage: you gain time and distance. Whether you use this to help a team member up, to heal or to make the last few meters to the safe room is up to you. Especially on maps with cars, the action-packed fight between the infected looks grotesquely epic. You have to see it. But be careful, the construction worker zombies with hard hats and those in fireproof suits are not attracted to the bile.

Why do you rarely see a tank pinned down by zombies? Because there's always someone who immediately throws a molotov after the boomer bile. Perfect move for getting kills, but tactically unwise because it can cost the whole team.