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