Two other games based on the same engine have been ported to Linux
Half-Life 2: Death Match and Day of Defeat: Source are two amazing titles, and now it seems they are slated for a Steam for Linux launch, which means that Half-Life 2 is getting closer.Half-Life 2: Death Match is probably one of the most entertaining multiplayer experiences in the history of gaming and Valve is considering bringing it to Linux.
The more interesting conclusion is that Half-Life 2 is not that far away because it uses the same version of the Source engine.
The announcement was made on the official Steam forums and it only implies that all Source-based titles such as Half-Life 2, both Portal games, and the Left for Dead franchise are near.
Instructions on how to install the two mentioned games, Half-Life 2: Death Match and Day of Defeat: Source, can be found in the same forum post.