While I'm sure whatever they show will be nothing of consequence, if you're a Halo fan, Reach seems like a legit experience rather than ODST which always felt more like a MS marketing scheme at $60.
New Real multiplayer. New engine. 3 years in development. Some fundamental changes to the core experience.
Like I said if you're a Halo fan that's what you want. Of course like with any series if you are burned out on it, then that's another issue but this seems like a legit full Halo experience rather than ODST which should have probably been a piece of DLC like the GTA DLC if we are talking value.