http://store.steampowered.com/app/362890/There was a topic on this in like 2008 or something, back when it was in early development. (This game is mostly done except for the Xen levels, but there is still a ton of awesome gameplay anyways)
Black Mesa is a HL1 remake in the source/half life 2 engine. It's on steam right now for $10.
I highly recommend this! It has great graphics and textures. It has all the same levels as half life 1 except a whole lot more detailed. You get to enjoy the half life 1 experience with the source engine physics and graphics. The music is absolutely stunning, I am fairly certain that the music is done by a man who work(ed) at valve on the half life games.



I currently am on, "On The Rail" chapter. I have really enjoyed the game so far, it does not feel like a mod. If you want reviews better than mine, check the steam reviews.