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