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