A lot of you are going to be anxious to play this mod so I'll make it quick. The first release of the very long-awaited Black Mesa mod is here. Although the mod has been Greenlit for distribution on Steam it cannot be downloaded from there just yet. The official downloads page can be found here and includes a Torrent option so you won't have to worry about download servers going down on you. The filesize is 3.8 GB and this release covers everything from the start of the game to the Lambda Core chapter.
The Xen levels and Black Mesa: Deathmatch are to come at a later date, along with full Steam support via Greenlight, which will include Steam achievements and other improvements. Keep an eye out for our video review, coming in the next few days.
Update: The website has unsurprisingly gone down but you can get a torrent for the mod here.