Well, I'd like to open with what I first mentioned, speculation.
Reach, in theory, is going to have to be totally different than Halo 3. A multiplayer beta is being released, so at least the online aspect is going to be different ( I. E. Marines instead of Spartans).
I hope it has what Halo 3 doesn't have much of now: classic fun. I want to play TS on Last Resort, I want Team BRs on Standoff, I want good old Halo style gameplay from when Halo 3 launched.
I fear for what ruined the 30 seconds of multiplayer fun for me: Forge Maps. No dissing the creators of said maps, a few are actually fun, and I'm sure a total crap-ton of work went into making them, but the truth is that they aren't good. They are unbalanced, too campable, poorly laid out,erc.
Anyway, I'm really hyped for this, and I cannot wait for what awesomeness will ensue.
[Edited on 09.08.2009 9:05 PM PDT]