To me, the double-press has always seemed akin to a force close. It's always seemed like an oversight to me whenever a game doesn't have an exit option. However, I didn't realize that this was the only way to rate games.
I really wish that there were a way to write reviews, maybe via the OUYA website that would then be pulled into the details page for a game (maybe just another button along with Play, Favorite, Move, and Uninstall). Ratings don't tell me much. A game might only have two or three stars, yet it might be a game I would actually enjoy. I would prefer to know why a game received the rating it did. It would definitely help me make a more informed choice, especially for games that don't have a demo.