One of the biggest potential stumbling points for the 360's (and PC's!) Game Room - having to secure an endless stream of ESRB ratings - has been solved in a fairly unique way by Microsoft.
Whereas similar platforms - like Nintendo's Virtual Console for the Wii - submit each game to the ratings board individually, Microsoft has had the Game Room itself classified, the virtual arcade given a E10+ rating.
This means Microsoft can release as many games on the service as often as it likes without having to submit them to the ESRB, which should not only speed up the delivery of titles onto the Game Room, but prevent ESRB listings from spoiling the fun in advance, something that happens all too often with Virtual Console titles on the Wii.
There is, of course, a catch, and it has the potential to be a big one for fans of certain titles: the "universal" rating means that no games rated over E10+ will be released onto the Game Room. While this won't affect the majority of the retro titles due to appear on the platform, it will affect a few of the biggest potential releases, like Street Fighter, Mortal Kombat and Metal Slug.
Still, those are in the minority, and as GamerBytes points out, you've probably already got them on your 360 in some form or another.