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