Other than the Valve games Linux will soon get Metro: Last Light and Football Manager 2014. Almost no AAA games so far, but it is to be expected that AAA producers are generally slower and more conservative.
From a technical standpoint, Wine is extended to make the game work, that version of Wine is bundled with the application, and a script is included to run it without further user involvement.
I don't get why people still insist this sort of port somehow doesn't count. If it runs at full speed, shows up as a "Linux game" under Steam, and the user literally can't tell the difference, what does it matter?