Here is the full list of all 50 Black Mesa achievements. It takes around 20-25 hours to unlock all of the achievements on Windows.
View the *other* secret ending.
Find each member of the missing research teams.
Defeat Nihilanth in under 4 minutes.
Escape the Gargantua’s Lair without taking any damage from Gargantuas.
Find the snack supply canister.
Get whacked into oblivion in the ledge fight.
Don't use the Cyanogen and let the Gonarch live.
Use Cyanogen to kill Gonarch.
Kill all Protozoans in the Borderworld.
Accept G-Man’s offer of employment.
Take out all three Healing Crystals in Nihilanth’s Chamber at the same time.
Cook a Grenade for too long.
Use the welcome mat.
Skip the opening Xen island with a secret jump.
Wait too long to jump into the Lambda Teleporter.
Die in the AMS Beam before starting the experiment.
Don't kill any Vortigaunts in the Borderworld.
Escape the Hangar in Surface Tension without alerting the Soldiers.
Assemble all the possible Scientists and Guards at the end of Office Complex.
Kill 10 Enemies with Tripmines.
Decline G-Man’s offer of employment.
Carry the Hidden Hat to Endgame.
Complete Interloper without taking any laser damage.
Deliver the finishing blow to Gonarch with your Crowbar.
Help the Barnacle and Headcrab find true love.
Drown in Lambda Core's coolant.
Kill an Icthyosaur with either the Tau or Gluon.
Conduct all of the questionable research experiments.
Overcharge it anyway.
Get killed by your own Snarks.
Kill a Barnacle with a Satchel.
Kill a Marine with their own grenade.
Use the alternate path in Office Complex.
Send the Hidden Hat to Xen.
Refuse to insert the specimen into the Anti-Mass Spectrometer.
Ruin the microwave casserole.
Interfere with the alarm and laptop in Anomalous Materials.
Use an entire clip of Gluon ammo in one continuous shot.
Kill a Controller without killing any of its mind-controlled Vortigaunt slaves.
Kill 5 enemies with one grenade.
Kill a Headcrab using fire.
Kill an Assassin with the .357 Magnum.
Kill 10 enemies with Snarks.
Kill 20 enemies with the Hivehand.
Kill 10 Airborne Headcrabs using the Shotgun.
Perform surgical caffeine extraction from 20 machines.
Headshot 20 enemies with the .357 magnum.
Kill 10 enemies with a reprogrammed Sentry.
Get overtaken by a Headcrab's ample anterior.
Pass the toilet paper to the scientist in need.