For me the best E3, like many others have said, was last year 2014. But for me it was because nintendo back in 2013 tried something new with a digital event and it wasent really that popular. For the most part it is because most people see this things at home and not at the press conference itself, so I understand the direction and reason behind it.
But then last year, with all the hate from the previous year, they still managed to have a greater E3 than the rest. The treehouse live was an instant hit that even MS is copying it this time, dont know about sony. They showed the best part of their games even if they had not many since third party ditched them and their creators coment on them. It was rehersed so we only saw the best trailers and jokes wich sometimes are a little underwhelming live on stage. It was short and sweet and the most of the content was shown in the treehouse and everithing with gameplay, NO CGI.
So yea, I loved it because nintendo improoved and solidifyed its new way of doing things and people responded positively and I just loved the new way things are going to be done. Who knows, maybe in a few years others will follow suit.
It takes genuine talent to see greatness in yourself despite your absence of genuine talent.