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