Leszek has shared that he's been quietly porting Darksiders to Linux and SteamOS. Darksiders is a third-person adventure "hack and slash" game. Confirmation on the Darksiders Linux port was made via Twitter.
Those curious for other details can see Wikipedia and their web-site.
Leszek was previously responsible for Painkiller: Hell & Damnation for Linux and other Linux game porting work.