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