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