Ok I think this mod is getting way too little praise. But it is also taking way too long to be released on Steam now so I'm going to share some screenshots and some of my experiences with the mod.
Let's start off with how much the game feels like Half-life. That is already a win in my book. You are still delivering what made the original so great without compromising on the source material. And then something happened that was not expected.
The mod actually starts writing in the lore from the next game to fill the gaps. Not just that but suddenly it gives NPCs in it more of a role and more personality.
Playing through the levels felt familiar, felt new, and felt much more streamlined. Half-life is one of those games where I would remember what happens around nearly every corner. And with that I also remember how boring some of those places would be. Black Mesa does a good job of removing those parts that just seem to drag on and convert them to something that feels like it makes sense without compromising what the stage was about. 2 instances especially felt like this. On a Rail and Surface tension comes to mind.
The game has managed to update and improve on what I remember from the original Half-life. It would be a worthy rerelease of a title if ever there was one.
More screenshots on my profile.