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