As promised by the team at Crowbar Collective around the 1.0 release, a Definitive Edition of Black Mesa is coming and there's now a Beta. This seriously impressive Valve-approved Half-Life re-imagining sure is something else, and it sounds like this huge update is going to make it even more exciting to go through it again.
The biggest part of the 1.5 update for Black Mesa appears to be going over all of the Earth levels, to bring them up to the detail level they pushed with the later Xen sections. Crowbar said they "implemented brand new art for all the outdoor environments, and refined the art previously seen in the Summer Beta".
On top of all the art updates, they're also improving the Steam Workshop integration so that it's a little less finicky to get going. With the Beta and eventual release, they've cleaned it up so all you should need is to hit the Subscribe button and it will all be sorted for you.
There's tons of little details added too like dynamic lights to all health chargers and HEV chargers, corpse gib sounds, Agrunt pod breaking sound effect, a crouch toggle UI option and lots of bugs fixed across the entire game, some of which were game-breaking. It's huge, full changelog here. For Linux especially, they should have now fixed a pesky crash bug in the Surface Tension section.
If you own it, simply opt into the "public-beta" on Steam from the Properties menu.
You can buy Black Mesa on Steam.