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.
Find each member of the missing research teams.
Carry the Hidden Hat to Endgame.
Accept G-Man’s offer of employment.
Decline 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.
Escape the Gargantua’s Lair without taking any damage from Gargantuas.
Complete Interloper without taking any laser damage.
Find the snack supply canister.
Kill all Protozoans in the Borderworld.
Don't kill any Vortigaunts in the Borderworld.
Kill a Controller without killing any of its mind-controlled Vortigaunt slaves.
Don't use the Cyanogen and let the Gonarch live.
Deliver the finishing blow to Gonarch with your Crowbar.
Use Cyanogen to kill Gonarch.
Get whacked into oblivion in the ledge fight.
Use the welcome mat.
Kill an Icthyosaur with either the Tau or Gluon.
Skip the opening Xen island with a secret jump.
Wait too long to jump into the Lambda Teleporter.
Send the Hidden Hat to Xen.
Use an entire clip of Gluon ammo in one continuous shot.
Drown in Lambda Core's coolant.
Escape the Hangar in Surface Tension without alerting the Soldiers.
Kill 20 enemies with the Hivehand.
Overcharge it anyway.
Get killed by your own Snarks.
Kill 10 enemies with Snarks.
Conduct all of the questionable research experiments.
Kill an Assassin with the .357 Magnum.
Kill 10 Enemies with Tripmines.
Headshot 20 enemies with the .357 magnum.
Kill a Barnacle with a Satchel.
Kill 10 enemies with a reprogrammed Sentry.
Help the Barnacle and Headcrab find true love.
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.
Cook a Grenade for too long.
Perform surgical caffeine extraction from 20 machines.
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.
Interfere with the alarm and laptop in Anomalous Materials.
Kill 5 enemies with one grenade.
Pass the toilet paper to the scientist in need.
Ruin the microwave casserole.