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