Internet sleuths will likely spoil many sometime in late May, so there's that to look forward to.

Sony will have a 2 hour presentation where they give a lot more details on games you already know about like Spiderman or KIngdom Hearts III. They will also tease a few new games but they won't be released for about 3 more years.

Nintendo will do something similar, but it will only take 1 hour. They will give more details on first party games games we already know about and maybe 1 - 2 games released this year that they haven't said anything about yet. They are also going to spend a lot of time talking about their online service and people will hate it.

Microsoft will give a 2 hour presentation where they give details on a bunch of games that are also coming out for PS4. They will also talk about a couple of first party games which are also available on PC. Then they will tell about all of these new features that no one really asked for that they are adding to Minecraft and their other first party games. All of these new features will also be available on PC. They will also use more buzzwords than Nintendo and Sony put together.

Bloodborne 2 announcement anyone? Maybe news about KH, FF7 or Shenmue too (less likely). Surely Red Dead news, they have the marketing deal? I expect GTA6 announcement after Red Dead release, so maybe at PSX...

We shouldn't have new teasers for very far away games, because the next generation of games will most likely be on PS5. So the studios will finish what they're already working on, and then move on the new hardware.

yeah that would be satisfactory unless they don't tell us anything about it and then its safe to assume its a PS5 game 

Across all the different companies, there will be a share of announcements to go around. Maybe 2-3 per showing.

As for the big main 3, I'm not expecting too much. Perhaps ranking in most announcements to least, I'd go Sony > Nintendo > Xbox

In terms of announcements quality:
Nintendo > Sony > Xbox

In terms of overall quality:

Sony > Nintendo > Xbox

Not much for Nintendo. They just have to show footage of Smash, FE, Pokemon, Metroid, Bayonetta 3. But I can see them announcing Animal Crossing and Pikmin 4.

Exactly five. Although it will balloon to around 40 if we take the booming Microsoft voice at it's word when it uses the term "exclusive".

about that. I can't really imagine the game releasing in anything after august. it has to be either July or august. 

i think there will be a Japan Studio game and some kind of third party exclusive, maybe Japanese too. I wouldn't expect much else. We are at that time now where any studio that has released a big game recently probably aren't even going to be seen again this gen, let alone be ready to announce anything