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