Half-Life is without a doubt one of the most influential titles in the history of gaming and now it's also available on Linux, with a 14-year delay.
Half-Life is based on a heavily modified Quake engine and has both Direct3D and OpenGL capabilities. A Linux release would have been possible a long time ago, but Valve probably never considered it.
In any case, Valve has decided to provide its fans with a surprise and release the original Half-Life on Steam for Linux. You might think that such an old game would have lost its appeal, but the people who grew up playing it will find it just as exciting as 14 years ago.
It's still in the beta stages and it still gives that ridiculous error “Node Graph out of date.” It also has some mouse issues, but they should be fixed soon.
In any case, here are some screenshots from the Linux version of Half-Life.