This is a really impressive remake, and one of the most impressive fan works I've ever seen from a production values standpoint. It does a really good job updating Half Life 1's level design, gameplay, and presentation to modern (aka HL2) standards, although sometimes the dated design of the original does still show through. Surface Tension is still too long and too combat-heavy, and the Lambda Complex teleporter maze is still extremely annoying. But otherwise it's generally real good. Most of it has a nice balance between being faithful to the original, and adding cool new stuff. It does feel like they tried to amp up the horror elements a bit, and they use lighting really well in service of that too.

And then there's the expanded Xen section, which has been massively reimagined and now takes up maybe 1/4th of the game time. In the original Xen was short, kinda empty, and fairly annoying. In Black Mesa, Xen is probably the best part of the game! It is extremely gorgeous, full of really cool and varied level design, some really neat setpieces, some interesting puzzles. Its very well paced. The atmosphere of it and how it builds the illusion of a whole alien ecosystem existing outside of just what you see heavily reminded me of Metroid Prime, and that is high praise from me.

So: the remake of HL1 is real impressive, but the original Xen section is absolutely excellent.