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