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