I thought ODST was the best installment so far, so Reach better carry over the same feel as that game or I am not gonna be impressed. I thought the game was much more immersive and also had more (HEY YOU CAN ACTUALLY DIE IN THIS ONE N00BS) reality.
I also liked the fact that the story engaged me. I think that Bungie got really obsessed with the multiplayer for a while and didn't give the actual game enough time and energy.
Either way, I think I will try the Beta just to check out the new modes and the new guns.