Nothing is true. Everything is permitted. Understand the meaning of these words. It matters not how we complete our task, only that it's done.
I think this will be a "traditional" Halo game in terms of of being an FPS and maintaining the core gameplay elements, but with that said I'm betting they are going to explore some creative new gameplay elements that will make it quite a different experience. Like with ODST, for example, they are featuring the low light vision mode for easier navigation and identifying useable equipment and objective items. I think the "how you experience a Halo game" is going to be what they're looking most at in terms of changing with this and any other future titles.