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