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.
As A Tank hit 20 Survivors with a car in the Crash Course campaign.
Dole out 5000 total Survivor damage as a Special Infected.
Win a Versus campaign of Crash Course.
Smoker pull a bile-covered Survivor until you hold him during Crash Course.
As an Infected, incap a Survivor who has entered and left a safe room.
Earn a Gold medal in Survival mode on any official level.
Pounce a Survivor for 25 points of damage in the Crash Course campaign.
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.
Kill a Witch with a single headshot.
Earn at least a Bronze medal on every official Survival level.
Earn at least a Silver medal on every official Survival level.
Earn a Gold medal on every official Survival level.
Survive all campaigns on Expert.
Kill 53,595 Infected.
Kill a Special Infected with an exploding barrel.
Revive 50 incapacitated Survivors.
Kill 5,359 Infected in the Crash Course campaign.
Headshot a Hunter while he's leaping.
No Survivors take damage after contacting the rescue vehicle.
Survive any campaign on Expert.
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.
As a Special Infected, incap someone who is trying to sacrifice themselves.
Your team wipes all Survivors after the escape vehicle has opened in Crash Course.
Restart the generator within 30 seconds of it shutting off.
Your team incapacitates three Survivors within five seconds.
Have all 3 generators running at once in "The Sacrifice" finale.
Kill all four Survivors on one life as a Tank.
Cover four Survivors with Boomer bile at once.
Constrict two Survivors on one life as a Smoker.
Catch a rare strain of infection, then pass it on to someone else.
Pounce two different Survivors on one life as a Hunter.
Survive the Blood Harvest campaign.
Survive the Dead Air campaign.
Survive the Death Toll campaign.
Kill an Infected with a single blow from behind.
Shove a Boomer and then kill him without him splashing on anyone.
Earn a Silver medal in Survival mode on any official level.
Earn a Bronze medal in Survival mode on any official level.
Single-handedly kill a Tank.
Sneak past all Witches in a campaign without disturbing one.
Play an entire campaign with no Survivors taking friendly fire damage.
Finish a campaign without ever using a first aid kit on yourself.
All Survivors complete a campaign without being vomited on.
Survive an entire campaign using only pistols.
Complete one round of Survival on The Last Stand.
Kill 10 Smokers as they are pulling helpless Survivors.
Have Bill sacrifice himself for the team.
Give pain pills to 10 Survivors.
Heal 25 Survivors with a first aid kit.
Light a Witch with a Molotov.
Punch a Hunter as he is pouncing.
Shove a Hunter off of a pinned and helpless Survivor.
Protect any Survivor from an attacking Infected 50 times.
Stun a Tank with an explosion in the Crash Course campaign.
Survive the No Mercy campaign.
Beat a campaign with all 4 Survivors.
Survive a campaign without being incapacitated.
Survive the Crash Course Campaign.
Rescue a Survivor trapped in a closet.
Kill a Witch without any Survivor taking damage from her.
Blow up 20 Infected in a single explosion.
Complete "The Sacrifice".
Kill a Tank without it dealing any damage to a Survivor.
Set 101 Infected on fire.
Light a Tank with a Molotov.
Make 100 headshot kills.
Heal a fellow Survivor when your own health is below 10.
Rescue a Survivor from a Smoker's tongue before he takes damage.
Kill a Smoker who has grabbed you with his tongue.
You or another Survivor take no damage after being vomited on by a Boomer.