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.
Don't kill any Vortigaunts in the Borderworld.
Get whacked into oblivion in the ledge fight.
Decline G-Man’s offer of employment.
Accept G-Man’s offer of employment.
Carry the Hidden Hat to Endgame.
Defeat Nihilanth in under 4 minutes.
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.
Escape the Gargantua’s Lair without taking any damage from Gargantuas.
Find the snack supply canister.
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.
Find each member of the missing research teams.
Use Cyanogen to kill Gonarch.
Kill 10 Airborne Headcrabs using the Shotgun.
Use the welcome mat.
Kill an Icthyosaur with either the Tau or Gluon.
Skip the opening Xen island with a secret jump.
Send the Hidden Hat to Xen.
Wait too long to jump into the Lambda Teleporter.
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 10 enemies with Snarks.
Conduct all of the questionable research experiments.
Overcharge it anyway.
Get killed by your own Snarks.
Kill an Assassin with the .357 Magnum.
Headshot 20 enemies with the .357 magnum.
Kill 10 enemies with a reprogrammed Sentry.
Kill 10 Enemies with Tripmines.
Kill a Barnacle with a Satchel.
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.
Perform surgical caffeine extraction from 20 machines.
Use the alternate path in Office Complex.
Kill 5 enemies with one grenade.
Cook a Grenade for too long.
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.
Pass the toilet paper to the scientist in need.
Ruin the microwave casserole.
Interfere with the alarm and laptop in Anomalous Materials.