Recent reviews by Red Menace

Black Mesa started out as Black Mesa Source, a free HL2 mod that sought to remake HL1 with updated mechanics, and in my opinion, it's a task they've managed to accomplish.
from the free mod release, to 2015 steam release, 2016 surface tension restoration, 2018 graphical updates, and 2019's long-awaited Xen Arrival, they've been iterating upon it to make it a vision of half life comparable to official, and Valve's endorsemnt of it shows that.
some parts of original got simplified, such as on a rail maze and we've got hostiles vents, but i think it helps the flow of the game better.
One thing of note I'd like to highlight is the soundtrack by Joel Nielsen, which manages to be in style similiar to HL2's, but have its own spin of melancholy, particularly the Xen segment remixes.
Combat.
much of combat has better feel to it than half life 2's, though I'd note that HECU are a bit too on the difficult side, due to using HL2's combine soldier AI, which was well made, but having higher health and accuracy, which makes them much more difficult of opponents.
Meanwhile, the uniquely crafted segments of Xen offer a much more movement-based combat reminiscent of doom games, where you dodge projectile-based attacks, and it's arguably the most fun I had in any half life game in terms of raw combat, unsupported by chapter mechanics.
Graphically, this game squeezes the most out of sourc engine, and looks really impressive at times.
Overall it's a worthwile way to experience events of Half Life 1 in a more modernized package.