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