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