A Bungie forum member by the name of P40L0 360 recently posted what seems to be some very insightful information about Halo: Reach. You know how Bungie forums members are though.. I would take this with a huge grain of salt!
-It’s an FPS, and not a MMO or similar (and ok)
-It’s more Multiplayer/Online oriented then previous Halo, and the SP Campaign will be something “different” to what we’ve seen so far with the previous games.
-The game is under development since after Halo 3, and for more time then ODST (that is developed by a small part of the team, and it was done in 1 year and an half)
-New graphic engine!
-The multiplayer will be different/new.
-It’s the “next big Halo” for Bungie and Microsoft, same importance as an Halo 4
-It’s everything “darker” and more serious.
-150 people are working on the Project since 2007