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