Bethesda: I didn't see
Microsoft: B
I didn't watch it completely, but from what I saw, it seems like it was pretty solid.
EA: D
The only really good thing from this presentation that comes to mind was Mirror's Edge which looks really neat. Unravel also seems to be like one of the few things of interest. Unfortunately, it wasn't enough. If you saw the press conference, you know what they focused on. Most of the presentation was bland and boring. Nothing much of interests.
Ubisoft: D+
Typical Ubisoft with typical games. Your usual Just Dance game with a god awful and unnecessary performance. Your usual Assassin's Creed game. Even though I love the franchise, it has lost its charm over the years and seeing a new game isn't a big event like it used to be years ago. Some nice additions such as For Honor which could be an interesting game.
Sony: B+ or A-
Probably one of the better press conferences. Uncharted 4 was great, we got some nice looking and interesting games such as Dreams & Horizon, which is honestly my personal favorite from the new games we didn't know about before E3. There's also Project Morpheus that could give gamers something good to play with. No Man's Sky looks fabulous and seems like it's going to be a huge game. We also got some other interesting games such as The Last Guardian, they showed Street Fighters V and Shenmue 3. Lots of good stuff along with some 3rd party games support.
Nintendo: C-
Most of the games we already knew about. There wasn't any big surprise for the most parts, it was disappointing. I can understand the kids being mad at the new Metroid game. Even though it doesn't look as bad as people make it seem to be. Too much focus on Super Mario Maker and too much focus on amiibos stuff. Star Fox Zero looks great at most, but it didn't really wow me. Overall, it was slightly disappointing and let's just say I had put my expectations pretty low.
I didn't watch the others.