There's some tasty info on Black Mesa: Source here, along with a nice teaser trailer. It's definitely looking sweet.

Here are some of the features:

* Redesign and overhaul of all 18 chapters, the hazard course and deathmatch levels of the original Half-Life and Half-Life DeathMatch games.
* Models now take advantage of increased polycount limits and normal mapping technology making deadly opponents and friendly coworkers appear more real.
* A completely original soundtrack and music library bringing Half-Life's themes and feelings to life in the new sounds engine built into the Source Engine.
* Artifical Intelligence that will hunt you by sight and sound.
* Normal, bump and specular maps built into textures giving flat surfaces a new, more dynamic look.
* Co-operative mode, allowing you and your friends to play through Black Mesa together.
* The entire cast and characters that the world fell in love with more beauty than ever before, bringing truth to the saying, "if looks could kill..."
* A multiplayer mode allowing for deathmatch and team deathmatch experience with the complete Half-Life 1/Black Mesa Aresonal at your disposal.
* A priority on gameplay and immersion factors such as sounds, functionality and interaction.
* Built by developers who's passion is seen through the quality of their work.

Thanks moddb.com!