Here is the full list of all 73 Left 4 Dead achievements. It takes around 60-80 hours to unlock all of the achievements on Windows.
Kill 5,359 Infected in the Crash Course campaign.
Kill 1000 Infected with a mounted machine gun.
Complete one round of Survival on The Last Stand.
Stun a Tank with an explosion in the Crash Course campaign.
As an Infected, incap a Survivor who has entered and left a safe room.
Cover four Survivors with Boomer bile at once.
No Survivors take damage after contacting the rescue vehicle.
Smoker pull a bile-covered Survivor until you hold him during Crash Course.
Earn a Bronze medal in Survival mode on any official level.
Survive an entire campaign using only pistols.
All Survivors complete a campaign without being vomited on.
Survive the Death Toll campaign.
Dole out 5000 total Survivor damage as a Special Infected.
Survive the Blood Harvest campaign.
Drag a Survivor 100 feet with your tongue as a Smoker.
Kill a Witch with a single headshot.
Sneak past all Witches in a campaign without disturbing one.
Survive the Dead Air campaign.
Survive the Crash Course Campaign.
Restart the generator within 30 seconds of it shutting off.
Pounce two different Survivors on one life as a Hunter.
Heal 25 Survivors with a first aid kit.
Revive 50 incapacitated Survivors.
Constrict two Survivors on one life as a Smoker.
Heal a fellow Survivor when your own health is below 10.
Headshot a Hunter while he's leaping.
Rescue a Survivor trapped in a closet.
Set 101 Infected on fire.
Leave a safe room to save an incapped teammate and bring them back safely.
Punch a Hunter as he is pouncing.
Light a Witch with a Molotov.
Blow up 20 Infected in a single explosion.
Shove a Boomer and then kill him without him splashing on anyone.
Give pain pills to 10 Survivors.
Kill a Witch without any Survivor taking damage from her.
Kill a Tank without it dealing any damage to a Survivor.
Win a Versus campaign of Crash Course.
Kill a Smoker who has grabbed you with his tongue.
Save another Survivor from a Special Infected while on the ground.
Make 100 headshot kills.
Catch a rare strain of infection, then pass it on to someone else.
Survive a campaign without being incapacitated.
Light a Tank with a Molotov.
You or another Survivor take no damage after being vomited on by a Boomer.
Kill 10 Smokers as they are pulling helpless Survivors.
Protect any Survivor from an attacking Infected 50 times.
Kill an Infected with a single blow from behind.
Rescue a Survivor from a Smoker's tongue before he takes damage.
Survive the No Mercy campaign.
Beat a campaign with all 4 Survivors.
Shove a Hunter off of a pinned and helpless Survivor.
Single-handedly kill a Tank.
Play an entire campaign with no Survivors taking friendly fire damage.
Finish a campaign without ever using a first aid kit on yourself.
Kill 53,595 Infected.
Survive any campaign on Expert.
Survive all campaigns on Expert.
Survive a campaign with no Survivors taking damage from Special Infected.
Kill all four Survivors on one life as a Tank.
Earn a Silver medal in Survival mode on any official level.
Earn a Gold medal in Survival mode on any official level.
Earn at least a Bronze medal on every official Survival level.
Earn at least a Silver medal on every official Survival level.
Earn a Gold medal on every official Survival level.
Your team wipes all Survivors after the escape vehicle has opened in Crash Course.
As A Tank hit 20 Survivors with a car in the Crash Course campaign.
Pounce a Survivor for 25 points of damage in the Crash Course campaign.
Your team incapacitates three Survivors within five seconds.
Complete "The Sacrifice".
Have Bill sacrifice himself for the team.
Kill a Special Infected with an exploding barrel.
Have all 3 generators running at once in "The Sacrifice" finale.
As a Special Infected, incap someone who is trying to sacrifice themselves.