I'm glad they finally finished that project. I remember playing the Sector-C Test Labs portion of Black Mesa many years ago (can't even tell when it was, probably as soon as they released that portion of the game for a public test). I thought it was very good back then. I'm pretty sure that the overall quality of the whole thing is good even today.
The reality - at least for me - is that despite the original Half-Life not aging that well, it still plays very smoothly and is still a fun game (sounds a bit like a contradiction, but what I mean by 'not aging well' in this case isn't related to the gameplay much, more about audio, physics and visuals). So the Black Mesa 'remaster', while not necessary to experience Half-Life, is a welcome version of it to bring the game to a more modern style and look for perhaps a new audience. Not necessarily for the younger generation, but even for gamers who never cared to play the game to this day even if they heard about it left and right back then when it was the craze.
I don't think I'll buy Black Mesa since I really don't mind just playing the original version. But I'm absolutely glad they've done it all and never abandoned the project. They managed to make more Half-Life content than Valve since Episode Two, that's saying something. Maybe Valve should hire them to make an actual new Half-Life game. If I was Gabe (or whomever is responsible for the Half-Life IP licensing stuff) I'd give them the green light to work on something of their choosing within the Half-Life franchise / universe, make their proposition if they have any and provide them a full complementary team to work on their game.
I'm happy for them.