Run. Think. Shoot. Live. Source. Black Mesa is the Half-Life 2 total conversion of the original Half-Life game. Utilizing the Source engine and its endless array of possibilities and powers, Black Mesa will throw you into the world that started the Half-Life continuum and introduced Gordon Freeman to the world as a gun-toting, bullet-dodging Ph.D. in Theoretical Physics.
I was trying to run the original Black Mesa mod on Steam but it kept crashing with an engine error, so I decided to mess around with the gameinfo.txt file and managed to get the mod to work again.
After you install the mod, download this fix and extract the gameinfo.txt file into the mod folder. Restart Steam and you should now be able to play the mod.
NOTE: This is only for the Black Mesa mod, not the retail version on Steam