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.
Don't kill any Vortigaunts in the Borderworld.
Escape the Gargantua’s Lair without taking any damage from Gargantuas.
Find the snack supply canister.
Kill a Controller without killing any of its mind-controlled Vortigaunt slaves.
Skip the opening Xen island with a secret jump.
Escape the Hangar in Surface Tension without alerting the Soldiers.
Kill 10 Enemies with Tripmines.
Assemble all the possible Scientists and Guards at the end of Office Complex.
Cook a Grenade for too long.
Die in the AMS Beam before starting the experiment.
Refuse to insert the specimen into the Anti-Mass Spectrometer.
Send the Hidden Hat to Xen.
Drown in Lambda Core's coolant.
Use an entire clip of Gluon ammo in one continuous shot.
Kill 10 enemies with a reprogrammed Sentry.
Kill 5 enemies with one grenade.
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.
Get killed by your own Snarks.
Kill 10 enemies with Snarks.
Kill a Headcrab using fire.
Kill an Assassin with the .357 Magnum.
Help the Barnacle and Headcrab find true love.
Kill a Marine with their own grenade.
Get overtaken by a Headcrab's ample anterior.
Kill 10 Airborne Headcrabs using the Shotgun.
Kill a Barnacle with a Satchel.
Headshot 20 enemies with the .357 magnum.
Use the alternate path in Office Complex.
Perform surgical caffeine extraction from 20 machines.
Pass the toilet paper to the scientist in need.
Ruin the microwave casserole.
Interfere with the alarm and laptop in Anomalous Materials.
Kill all Protozoans in the Borderworld.
Carry the Hidden Hat to Endgame.
Wait too long to jump into the Lambda Teleporter.
Use the welcome mat.
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.
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.