Better late than never, I guess. Bioshock 2 has finally (more than two years after the PC release) arrived on the Mac as a port from Feral Interactive. This one is the sequel to the classic title from Ken Levine (who's currently working on the next game in the series, Bioshock Infinite), and while it's not quite as good as the original, it does add some new elements to the gameplay, and if nothing else, will return you to Rapture, the ruined underwater city that's been one of the most fascinating settings in video games over the last decade or so.
This version also contains the Fall of Rapture multiplayer game, so you can face off against other players online if you like. The price is $30.99, and you can grab the game from Feral Interactive directly, or pick it up on the Mac App Store.