There is a fairly large contingent of gamers who believe that Treasure’s Ikaruga is the greatest vertically-scrolling shooter of all time. Currently available only through the Xbox Live Arcade (though originally released for the GameCube), Ikaruga might be available on Steam in the very near future.
The PC version of Ikaruga is in development at Treasure and will be based on the XBLA version. Because the company has yet to publish a game through Steam, Ikaruga’s Steam Edition will have to go through the Greenlight process. But the “Yes” votes are already pouring in because it’s the greatest vertically-scrolling shooter of all time (obviously, I’m part of that large contingent).