I think that if you get your hopes up to high, you'll only end up dissappointed. For the past couple of years I hear journalist tell about some of the games they are expecting and especially the rumors, thinking they are facts. They get all hyped up and then when the E3 is happening they end up all dissappointed, because they expected more.
What I expect of the great three is:
Nintendo: Will show some new peripherals for the Wii/DS that should give some new control to playing games. A lot of games marketed to gamers of all ages and the newly dubbed casual gamers. Maybe a few so-called hardcore titles like Mario and Zelda. The press is probably whining to see something of the 'new' Kid Icarus.
Sony: will come with their new motion sensing controller like they have something revolutionary. Showing the same goddamn sport demo's and minigames, that Nintendo showed years ago with the Wii and Wiimotion plus. A number of titles for the PS3 that show of how beautiful the graphics are and that they serve the hardcore audience with sequels to existing titles. Furthermore some minor titles for the PS2 in hope to lengthen its lifetime with another year. The PSPGo and the Playstation network will be shown what for old new stuff it can expect.
Microsoft: Will act as if they just invented the wheel, with Project Natal. Show of some more of how good it is and what you can do with it in a Eye Toy like fashion. Then have some big titles, that are either sequels to other games, and maybe a new title (which is probably cross platform). They show of how well PC gamers can play with xbox gamers through their live network. Where Sony and Nintendo have handheld titles, MS will show some PC titles. Oh yeah, do not forget that some celebrities come on stage to say high for a few seconds and leave again (remember the Beatles).
Off course all three of them will also show the sales figures and remark about how much better they are doing than the competition. Which is okay, because the E3 is actually for the industry partners and shareholders, instead of the consumer.
All in all it doesn't have to be bad, they can still show some awesome stuff. But my point is, don't get to excited, because you most likely end up disappointed due it not meeting up to your expectations.