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