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