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