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.
Win a Versus campaign of Crash Course.
Smoker pull a bile-covered Survivor until you hold him during Crash Course.
Pounce two different Survivors on one life as a Hunter.
Shove a Boomer and then kill him without him splashing on anyone.
Catch a rare strain of infection, then pass it on to someone else.
Drag a Survivor 100 feet with your tongue as a Smoker.
Constrict two Survivors on one life as a Smoker.
Complete "The Sacrifice".
Have Bill sacrifice himself for the team.
Have all 3 generators running at once in "The Sacrifice" finale.
Kill a Witch with a single headshot.
Revive 50 incapacitated Survivors.
Play an entire campaign with no Survivors taking friendly fire damage.
All Survivors complete a campaign without being vomited on.
Finish a campaign without ever using a first aid kit on yourself.
Survive the Dead Air campaign.
Heal 25 Survivors with a first aid kit.
Restart the generator within 30 seconds of it shutting off.
Heal a fellow Survivor when your own health is below 10.
Headshot a Hunter while he's leaping.
Save another Survivor from a Special Infected while on the ground.
Earn a Bronze medal in Survival mode on any official level.
Protect any Survivor from an attacking Infected 50 times.
Set 101 Infected on fire.
Blow up 20 Infected in a single explosion.
Complete one round of Survival on The Last Stand.
Survive the Death Toll campaign.
Survive an entire campaign using only pistols.
Kill 10 Smokers as they are pulling helpless Survivors.
Survive a campaign without being incapacitated.
Light a Tank with a Molotov.
Survive the No Mercy campaign.
Punch a Hunter as he is pouncing.
Sneak past all Witches in a campaign without disturbing one.
Kill an Infected with a single blow from behind.
Shove a Hunter off of a pinned and helpless Survivor.
Leave a safe room to save an incapped teammate and bring them back safely.
Make 100 headshot kills.
Kill a Smoker who has grabbed you with his tongue.
Survive the Crash Course Campaign.
Light a Witch with a Molotov.
Rescue a Survivor from a Smoker's tongue before he takes damage.
You or another Survivor take no damage after being vomited on by a Boomer.
Kill a Tank without it dealing any damage to a Survivor.
Beat a campaign with all 4 Survivors.
Kill a Witch without any Survivor taking damage from her.
No Survivors take damage after contacting the rescue vehicle.
Give pain pills to 10 Survivors.
Rescue a Survivor trapped in a closet.
Single-handedly kill a Tank.
Kill 1000 Infected with a mounted machine gun.
Kill 53,595 Infected.
Survive any campaign on Expert.
Survive all campaigns on Expert.
Survive a campaign with no Survivors taking damage from Special Infected.
Survive the Blood Harvest campaign.
Cover four Survivors with Boomer bile at once.
Kill all four Survivors on one life as a Tank.
Dole out 5000 total Survivor damage as a Special Infected.
As an Infected, incap a Survivor who has entered and left a safe room.
Earn a Silver medal in Survival mode on any official level.
Earn a Gold medal in Survival mode on any official level.
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.
Kill 5,359 Infected in the Crash Course campaign.
Your team wipes all Survivors after the escape vehicle has opened in Crash Course.
As A Tank hit 20 Survivors with a car in the Crash Course campaign.
Pounce a Survivor for 25 points of damage in the Crash Course campaign.
Stun a Tank with an explosion in the Crash Course campaign.
Your team incapacitates three Survivors within five seconds.
Kill a Special Infected with an exploding barrel.
As a Special Infected, incap someone who is trying to sacrifice themselves.