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