Nintendo will announce a handful of titles that appeal mainly to Nintendo fans, and utterly disinterest people who don't care about Mario. Bit more on Bayonetta 2 and Wonderful 101, and maybe at least a hint on what Retro is up to, but the bulk of interesting stuff will be third-party stuff on 3DS.
Sony will show the actual console, a bit more on the games we've already heard about, and some of the larger companies will step up to reaffirm their support without really showing much. Probably too much emphasis will be spent on Killzone and Infamous, with only vague notions of more games on Vita and little to adequately demonstrate this.
Microsoft will unveil their new console, and we'll collectively 'meh' because it's an overblown kitchen sink product like Windows 8. They'll attempt to emphasize connectivity with smartphones, and 'innovation' with Kinect, but simultaneously alienate both hardcore and casual gamers.
Short version: We won't see anything worthwhile from anyone until first quarter of next year, and in the meantime, it'll be a lot of vague comments involving buzzwords like immersion and innovation. Sony has the advantage, provided they don't fuck up and massively overprice the PS4 - anything over $400, maybe $450, and they'll be in a very bad spot.
Idk. I've seen enough console launches now that if I've learned anything, it's that these are the times that matter least. It always, always will come down to games that catch on with people, smart marketing, and overt cost of ownership.