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.
Find each member of the missing research teams.
Deliver the finishing blow to Gonarch with your Crowbar.
Kill all Protozoans in the Borderworld.
Don't use the Cyanogen and let the Gonarch live.
Use Cyanogen to kill Gonarch.
Complete Interloper without taking any laser damage.
Don't kill any Vortigaunts in the Borderworld.
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.
Get whacked into oblivion in the ledge fight.
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.
Escape the Hangar in Surface Tension without alerting the Soldiers.
Overcharge it anyway.
Kill 10 enemies with Snarks.
Kill an Assassin with the .357 Magnum.
Kill 10 Enemies with Tripmines.
Help the Barnacle and Headcrab find true love.
Kill a Barnacle with a Satchel.
Kill 5 enemies with one grenade.
Cook a Grenade for too long.
Use the alternate path in Office Complex.
Assemble all the possible Scientists and Guards at the end of Office Complex.
Refuse to insert the specimen into the Anti-Mass Spectrometer.
Die in the AMS Beam before starting the experiment.
Perform surgical caffeine extraction from 20 machines.
Pass the toilet paper to the scientist in need.
Ruin the microwave casserole.
Interfere with the alarm and laptop in Anomalous Materials.
Accept G-Man’s offer of employment.
Decline G-Man’s offer of employment.
Use an entire clip of Gluon ammo in one continuous shot.
Kill a Controller without killing any of its mind-controlled Vortigaunt slaves.
Find the snack supply canister.
Kill 20 enemies with the Hivehand.
Kill an Icthyosaur with either the Tau or Gluon.
Conduct all of the questionable research experiments.
Get killed by your own Snarks.
Headshot 20 enemies with the .357 magnum.
Kill a Marine with their own grenade.
Kill 10 Airborne Headcrabs using the Shotgun.
Kill 10 enemies with a reprogrammed Sentry.
Kill a Headcrab using fire.
Get overtaken by a Headcrab's ample anterior.