Microsoft will make a big deal about something that no one will care about and will be largely ignored, but will still have enough wowswers stuff that they arent pushing yet that it wont really matter too much. There will be no mention of their Games for Windows beyond the plastering of the logo on games that are being pushed on 360.
Sony will show lots of great new stuff, lots of their old franchises that we're all waiting for, and some system changes that are not really all that compelling to anyone. They'll do something with the PSP but it wont amount to anything.
Nintendo will try to seem hip and cool to the hardcore and casuals and they will fail miserably. It will not matter though because critical acclaim is now irrelevant to Nintendo. They'll show a brief sizzle reel that will wow the dwindling hardcore gamers they do have.
The Third parties will show us all the real good stuff and will rise to conquer the earth as we know it. Which it turns out is in fact just a lot of basements in very small sections of urban centers. Weird.
There you have it. I spent all of like 5 minutes thinking those up so if they turn out to be right I demand worship.