E3 is, at it's heart, a trade show. So in theory just about anything could show up, especially if you're looking to farm out your project for funding/publishers/etc.
The hype engine and bullshit surrounding the trade show doomed it. It already killed itself off once the year after the Wii/360/PS3 debut debacle.
If you don't remember, I was there, so I'll sum things up: The 360 made a big splash and got lots of coverage, the Wii literally had lines stretching around the convention hall (people would wait 8 hours to play the Wii for 5-10 minutes to evaluate it), and the PS3/Sony booth, which cost around 12 million dollars to set up according to rumor... was empty. Oh people were in there, but I remember sitting up in NovaLogic's little room overlooking the trade floor and seeing the line form and stretch past Sony for people waiting to get in to try the Wii. The next year, Sony said they were taking their ball and going home. Like a week later Microsoft said "hell if they aren't doing it neither am I" and pulled out of E3. Nintendo pulled out shortly thereafter, and E3 collapsed that year into a series of "quiet, low-key press conferences in hotel meeting rooms around the city. I think it stayed that way for another year or so and then tried to come back, and has been kind of a zombie ever since.
E3 was... how do I describe it? Imagine the entire strip of Las Vegas crammed into one building. It was THAT much sensory overload. I met every game designer I ever had a professional crush on in one day. I saw projects years away from completion (I spent an hour discussing Hellgate London with the devs before there was even any alpha work, just some concept art). LA strippers were everywhere in all kinds of cosplay. The japanese companies I think flew cosplayers out to flirt with people at E3. The swag bags were insane. The last year I went, there was a tattoo artist doing ink, with the caveat that they had to tattoo G4's logo somewhere in the art. Even with that caveat the time slots for getting inked would fill up in minutes.
One year in the basement they had a 30 year retrospective of video games, including the most bitchen arcade selection of old 80's games you could imagine. I held court on the Joust machine undefeated for about an hour and was God of the Universe.
I played an 8-player Steel Battalion tournament. Which if you remember Steel Battalion, was almost impossible to get *two* people to play in. But Microsoft set up an xbox live server locally so everyone could play. It was beautiful.
For America's Army the US Army suited you up in a bullet proof vest, a helmet, and gave you an M4 with working bolt action for recoil and had you storm a shoot house. I still have the Polaroid they took and gave to me.
I fucking played Starcraft: Ghost, and it was a nearly finished product at that point.
And I was part of the problem. I had hookups, and passed a *lot* of business cards out for IT infrastructure, but it really wasn't aimed at me. It was meant to be a trade show. But the outside hype grew and grew and it became a TV and media event and grew to absurd levels. It was trying to be a trade show and a spectacle to help break into mainstream at the same time, and the hundreds of millions of dollars spent on parties, booths, swag, booth babes, and everything else made it top heavy.
Is E3 as psychotically amazing as it was? No. But perhaps that's a good thing. I went 3 or 4 times through various hookups, and I'm glad I went, and got to go at the absurd height of the craze. I'd go today if I got the hookup, because it'll still be kind of delirious. All trade shows are. But it won't have the same surreal quality as back when passes *started* at 400 bucks a head.