The two games worthy mentioning that were pushed out to the public for Steam Linux users are Counter Strike: Condition Zero and Wargame: European Escalation. There were also some other new titles pushed, but these are the two noteworthy additions. The full list of Linux titles can be found via the Steam Store.
Counter Strike: Condition Zero is a multi-player follow-up to the original Counter-Strike game. Condition Zero also features a single-player mission and bots. The game has been available to Windows gamers since 2004, but now nearly a decade later it's been pushed to Linux. This is a native Linux port of another Valve "GoldSrc" engine game after Counter-Strike 1.6 and the original Half-Life.
Valve will be bringing a majority of their games (if not all) to Linux in preparation for the Linux-based Steam gaming console. Counter-Strike: Condition Zero is currently considered beta on Linux.
The other game released for Linux today is Wargame: European Escalation, which was talked about at the beginning of the month as coming to Linux. Wargame: European Escalation is a real-time strategy game that was first released for other platforms in 2012. This game has been in semi-private Linux beta for the past few weeks but is now available to all Steam Linux gamers.