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