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.

VGames says

10/10 - Agree (3) Disagree

This was without a doubt the greatest mod that I have ever played. The entire thing felt so polished and professional that it really felt like I had bought a $60 AAA title. Excellent execution and great pacing. I was never bored. Truely a legendary mod.