This has been shown off a few times at SuperHappyDevHouse lightning talks doing livecoding demos. The ability to pause the game you're working on, edit attributes and resources, and resume the game is neat (and needs to be shown off better).
I've used this for a few small games I cranked out at the South Bay Game Jams. Being able to edit the code in the online IDE and see the changes immediately in the running game makes it really easy to tweak the gameplay.
This is great. And there are obvious paths to export games for mobile devices so this could be the best cross-platform development environment for 2D games.<p>The hardest and most time consuming part of game development is iteration and livecoding makes that so much easier.