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