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