Smash, Yoshi, Fire Emblem... these three will most certainly be there and they will be the main focus of the presentation.
That being said, Metroid Prime 4 and Bayonetta 3 have lots of chances of being showed as well... but since these titles are relatively early in development, we would get just a trailer.
We should also expect two or three new announcements. I mean, this is E3 after all. I could see them showing a big third party exclusive game and one or two new first party titles. Pokémon or Animal Crossing would be nice bets. I also would like to say that the new Retro Studio's game might see the light at last... but since every year we say the same and it never happens, I'll remain skeptical about that one.
All in all... I think Nintendo will have a great E3. Even if they only show things we already know they're coming, given what those titles are (Metroid, Smash, Bayonetta, Fire Emblem...) many people will be quite happy with just that. But if they add some new things to the table, it will just get even better. There's no way this will be bad. At worst, it will be decent. At best, it can be one of the best recent E3s for Nintendo.
