As others have said, this is not an open front end at all, it's a pay-to-play platform for Windows and Xbox 360 using Xbox Live and the Microsoft Points system. I actually have it on my 360. It allows you to create a virtual gameroom complete with decorations and arcade cabinets that you purchase. It's not as great as it sounds.
It's actually a very shallow, glorified menu based system. The amount of customization available is very limited. You're not exactly building anything truly unique to you. For a virtual game room it's not as intuitive as you think. The 3DArcade front end is much better.
Even the selection of games is a bit awkward. Just some pre-'85 stuff from Konami, Atari, Activision, and Intellivision. I believe that's it. Some are good classics, most are forgettable. The Atari collection is pretty good actually. They could add a lot more games from a lot more companies and consoles if they want, the thing is Microsoft chooses to sell the real good retro stuff from companies like Namco, Sega, SNK, Williams, Taito, and more notable stuff from Konami seperately on Xbox Live Arcade for more money with enhanced features and all.
I had high hopes for the idea and imagined something similar to the Wii Virtual Console as far as a massive selection of retro classics, set in a virtual customized game room and arcade where I can walk around, chat, play against friends and others, and even explore other custom game rooms and arcades. Instead it's a pretty shallow "front end" for a few decent Atari games. Skip it.