The new issue of Develop Magazine has a great interview with Bungie Studio manager Harold Ryan on the split with Microsoft. In it Harold admits that Bungie has a new IP in development - a game that was prototyped by 20 employees alongside the development of Halo 3. He also has this choice quote on why Bungie is better than "other developers that publish with Microsoft"
We want to be seen as different from the other developers that publish with Microsoft. As far as we believe it, we make better games and they are better quality in user experience across the board.
Epic, what say ye? Develop Magazine Interview with Harold Ryan