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.