I only watched the MS and Sony conference so that's what I'll give a descriptive grade on, but judging by what I know EA and Ubisoft showed I can at least give them a grade based on the games.

MS: B+
Positve: Everything MS showed was game focused. It was just a constant stream of game after game and I actually really enjoyed the entire show and didn't feel bored at any point and time. Most of the games they showed were exclusive and there were a bunch of reveals we didn't know about. MS showing support for the 360 later on and giving away two free games each month until Xbox One releases is nice.
Negative: The price of $499 is kinda step. Cheesy dialogue at times. Some tech issues.

Sony: B-
Positive: Most will agree that the biggest part of Sony's conference wasn't about games, but talking about no online requirements and no used game issues. A big kick in the balls to MS. Sony showed a pretty good helping of games for the Ps4 and proved they still will provide plenty of quality exclusive games for the Ps3 as well. The indie support is definitely there. Not to mention FF15 and Kingdom hearts 3 were bomb shells. The price of $399 is definitely a sweet spot.
Negative: There was a 20-30 minute period I was bored. Sony did show a lot of games, but most are multiplatform, even there two biggest bombshells are. Sneaking in the pay to play online after the price and drm reveal was tricky, but I caught it ;) Tech issues as well.

EA: B+
Ubisoft: B
Nintendo: B-

No ones showing was bad, just some slightly better than others.

Well. I would give MS a 6.5/10 because most of the stuff was OK at best. Dead Rising 3 was OK, KI3 looked stiff, but the new Halo looked interesting to say at least. I give Nintendo 8.5/10 because I liked most of the stuff they showed. Didn't care about Wii Fit U and Wii party U. Finally, I would give Sony a 8.5/10 as well. The original score was 9.5, but after finding out that KH3 and FF15 are not exclusives, I was kinda sad.

MY favorite was Nintendo's.

All of the other conferences showed someone with a gun shooting something or a yearly game with minor changes.

i enjoyed microsofts conference thought it was done well,personally sony $399 was the main thing at e3 but doesn't seem to get mentioned much out of everything else rumbling on

Didn't see Nintendo's because I was watching Sony's on delay

4) Ubi - Showed some decent games, but their main showings of AC IV and Watch_Dogs were at Sony not there. The Crew looked interesting, though not that amazing. The Division was a good ending. So overall, a lot of stuff I didn't really care about, nothing amazing, but some decent games

3) Microsoft - This was just a good solid conference. There were tons of games, including the impressive Titanfall and most importantly, they just kept the games coming. It does lose marks for Project Spark not really because of the game, but mostly because of the appalling banter. But there were no games that made me go wow, though I quite liked the look of Ryse and I REALLY liked the way the handled the Halo reveal. I don't like £429

2) Sony - So they lose points for the slow opening and the lack of Vita titles. They lose points for not really bothering to show their already announced games, how much better would that conference have been if they had the inFamous gameplay? I must say, I don't really care about the indie games and while I am not hugely bothered about the used games stuff, I did enjoy hearing everyone yell Sony Sony Sony!

What Sony did well was show off 3rd party games with interesting footage notably Destiny. They unveiled a very good looking console at a good price

Oh and they kind of re-announced FF and announced KH3. If either of those had any sort of release date, then they would have won

1) EA - So firstly, they kept their pointless celebrities to a minimum for their standards, but they had a series of genuinely impressive games. I thought the Sports games look good and then I was genuinely impressed by the Rivals, which did really surprise me

The key here was they had the most wow moments. That collapsing skyscraper!?!?!??! I know these next 2 have the same problem as Sony, but they are even more exciting and I know that EA will actually release them. So basically, the winners of E3 were the reveals of Mirror's Edge and Star Wars Battlefront. This was the only conference (apart from the Squeenix bit) that really got me out of my seat and very excited

I'll only do the big 3.

Microsoft: 8
positive: Exceptionally well paced, a ton of new game announcements, good demonstration of X1s graphics, ton of exclusives, started big, ended big.
negative: Not enough impressive gameplay, annoying and cringe worthy presenting skills.

Sony: 7.5
Positive: Brilliant down to earth presenting, a nice amount of games+demos, lots of indie games, some surprises, (The Order, KH3, FFXV), good pricing and crowd pleasing DRM speech.
negative: Poorly arranged and overly long, not enough new game announcements or exclusives.

Nintendo: 6.5
Positive: Lots of exclusives, had a some impressive showings mariokart, X, lots of gameplay footage.
Negative: suffered from being pre-recorded (lack of energy/soul), No surprise game announcements, No amazing trailer/gameplay demos.

I believe the Ubisoft press conference showed a small child in a red jacket... Though for not anywhere near enough time

On a different note, I'm trying to compare what system (PS4 or XBO) has the better exclusive lineup. Most of Sony's exclusives were revealed at the PS4 event back in February, so Sony's PS4 unveilings at E3 were not all that impressive. That said, I really liked what they're doing with the console. the price is right, the Eye is optional, they are supporting indies, they support used games and are anti-DRM, and PSN+ is better than Live Gold. As for the cons, the only thing I DIDN'T like was how they were sneaking in a pay 2 play online model with the system. it doesn't personally bother me since I feel PSN+ is worth it even without that requirement, but I know folks who are not going to like it and I do think it was a bad decision.

So far, for exclusives, can we get some comparisons? I know Sony has inFamous, Killzone, Knack, The Order, Drive Club, and...erm, that's all I can think of. Microsoft has Ryse, Sunset Overdrive, Titan Fall, Curse of Brotherhood, Killer Instinct, Forza 5, Quantum Break, D4, and Project Spark. I think at this point Microsoft certainly has MORE, but based on what I'm seeing, only Foza will likely end up top notch, whereas I think Infamous, Killzone, AND the order will all be very good. That is, based on history and the pedigree of the people making the games.

Nintendo will always be Nintendo. Mario games. Metroid Games. Zelda Games. donkey Kong Country games. Pokemon Games. It doesn't matter what happens, we will always love nintendo as long as they maintain their franchises.

However, the PS4 is the system that has the most appeal tome. Unlike most, I actually have and love a Vita, so I will be able to take advantage of all the system's features, and I'll be getting all the multiplatform games on PS4, since I see no reason to play games on the Xbone when I have a cheaper, more powerful alternative without restrictions on used games and DRM.

Conference wise I think it was really close. Overall, at this point, I just don't see any reason to get an Xbone. it's more expensive, the games look good but not enough to overcome the DRM and used games policies, and the system has less RAM and processing power to work with (3 gigs of ram on Xbone are used for the Kinect, OS, and UI, and only one gig is used for the UI and OS on PS4)

SONY - 8/10 I know that it was a big PS4 unveil and that everything was focused on PS4, but showing at least one new PSV game would have been nice. At least for us - devoted PSV fans. I was waiting the whole conference for either a glimps of new Naughty Dog game or SSM game, but sadly that never happened. They showed more of the games that we saw in February and while they look great I was kinda let down. I wanted to see more. The Order looked great, but I kinda hopped for more... Anyway it was a great PR show overall.

EA - 5/10 ES Sports bore me to death, and only thing that I loved at this conference was new too short Dragon Age trailer.

Microsoft - 6/10 The conference was great paced, and it was entertaining.... But. Project Spark is LBP 4 years after, TitanFall is reskinned COD, BF4 will be on everything else... Dravatar? LOL

Ubisoft - 8/10 Worst presenters, best game lineup. The weirdest moment of E3 was when Yves came on stage and stood next to Aisha.... AWKWARD! Anyway The Devision looks great, WatchDog amazing, SplinterCell good enough and of course Rayman is must buy.