I've been to E3 before PAX existed, and this year I'm at PAX Prime (And PAX Dev), and it's been a totally better experience all around.
1. No booth babes - don't get me wrong, I love the female form, but there's a huge difference between PAX fans of all shapes dressed up in what they genuinely want to, with real life behind it, and the going-through-the-motions gals hired at E3. Don't get me wrong - companies still specifically hire marketing girls between 20-30 from agencies in a lot of cases, but the lowered sleaze factor helps in making for an environment where nerd-sexy can thrive - and I fully support that.
2. Parties are way better. I remember the Rockstar events at E3, and so on - but just last night, I came from a creepy, but superb costume party held in a Mansion clone of the level they've been demoing, compete with a rather well-done ARG - it was certainly money wasted that really should have gone into the development, but as long as these companies waste the money, I did find the whole experience far more compelling than "here's some drinks and music and trailers, don't you think we're cool."
3. The folks are really a functioning community. Any time there's a slack, of someone's having a hard time, you'll find a lot of humanity there. I left my laptop in a room on the first day, and a chain of people helped make sure it got to the lost-and-found - and that's just a tiny story. "Don't be a dick" is still in its functional golden era there, and it doesn't look like it's faltering soon.
Don't get me wrong, there's plenty of healthy skepticism and differences in opinion, and hardships exist all over (mostly from 70,000 people), but it all works remarkably well. Enforcers (small army of volunteers) helps too.
Final day is tomorrow - bittersweet and exhausting, but still awesome.