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