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