This is a big E3 for Microsoft as they appear to have lost a little bit of steam since last year. Last year's press conference,while not bad. did not light the world on fire the way the ones from Sony and Nintendo did. It's also a big press conference because we'll finally see how many of the rumors (motion control, new dashboard, new Halo game, etc) are actually true and how much is fanboy speculation and misdirection.
Personally I'm hoping we get some news on
Alan Wake,
Scene It 2 (or a content pack), and maybe a new IP or two