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