I remember attending E3 2010. Got discount tickets through my school. Was really cool and I am sad I never got to go again. Being able to try out cutting-edge technology, chat with Robin Walker from TF2, 1v1 against the best Unreal player (forgot who that was its been a while) (we would get a t-shirt if we killed him even once, I got close with a cool mid-jump-launcher-thing melee but just missed) and seeing upcoming titles that never actually were released, was one memorable experience.
Definitely more showy but I did kinda prefered GDC 2011 where I got to meet our very own Packer and Ben Garney, which was cool too.