Want to feel old? The original Half-Life has turned 20. Valve released its definitive shooter on November 19th, 1998, both stretching the possibilities of the genre (both in technology and storytelling) and laying the groundwork for the company's gaming empire. But it's not Valve celebrating the momentous occasion -- instead, it's up to the fans. Crowbar Collective has released a trailer for the final portion of its Black Mesa remake, introducing its take on the strange Xen dimension that ends the first Half-Life game.