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