What Is it like a.k.a Should you go?
Spoiler: Yes. Even though I only had the cheapest and most limited Expo Pass, it was still an invaluable experience. I saw cool things, met awesome people, learned from the sessions, demoed my game (without a booth!) getting lots of constructive feedback, and really re-sparked my gamedev inspiration. The cost may be steep, but if you approach it right, it will be well worth the money.
The first two days (which I missed) are mostly sessions, panels and roundtables. If the ones I got to attend are any indication, they are awesome and highly informative. The Expo Floor opens up on day 3, where big names (like Epic or Unity) showcase their latest tech and can answer all your nitty-gritty technical questions. Lots of game booths will give you a sneak-peek at what's coming, and numerous companies will demo their latest tech gadgets, from alternative VR headsets to powergloves. There is also a pretty big Career Center for those looking for work/internships or learning about the industry.
Here's the Tips
Before I begin I must give a shoutout to JC Santiago from Granade Tree Games who taught me a lot of these and generally made my time at the GDC awesome. If the idea of a turn-based strategy with ingenious Scifi-Meets-Revolutionary-America theme appeals to you, check out their Outland 17!
Get Comfortable Shoes
You will most likely spend all your time on your feet and walking. Make sure you are ready!
Talk to Anyone
Waiting in line? Watching a demo? Odds are there will be other Devs around you, so speak up and start talking, that's half the point. No one will mind, and you might make some great friends or useful connections you didn't even expect.
Have a Game? Show it!
I don't care you didn't get a booth; set up your laptop on the couches or tables and ask passerbyers to check it out. Not only is it a good way to practice your marketing elevator-speech but you will get a ton of constructive feedback. Many folk are designers, so they know what to look out for. And it's a good segway to meeting people as well (see above).
Ask About the Tech
Comapnies like Unity, Crytek and Epic willl be demoing their latest engines with the devs right there, so take advantage of it. I had a chance to play with their engines and ask about implementing certain systems/mechanics, which gave me a lot of insight into what tech to use in the future.
Expo Closing Doesn't Mean the End
Check out @GDCParties or Meetup to find a lot of after-parties and events, make sure you sign up well in advanced since many have limited tickets. It's another great way to meet devs, get some free drinks and unwind.
Aside from getting a pass, working at GDC will make meeting people a bit easier and expose you to some after-Expo hangouts for the staff. I talked to one of my my friend who worked there, and really wished I signed up.
Most Importantly - Have Fun!
Take some time to enjoy the upcoming games and play with the new gizmos, even if it means waiting in line for a bit. The environment and the people can be a great source of inspiration and motivation for your future projects.