Flying a quadcopter is fun, but what is really fun is flying first-person view (FPV) and then joining up in group races. FPV by itself is pretty fun as-is but when you are with a half-dozen or more other people flying virtually through a forest at 30mph or more dodging trees and each other, it's absolutely amazing.
Something like this:
https://www.youtube.com/watch?v=70pusNNunMA
...except with more people. I fly with my co-workers at lunch at work in a little forest in the back and it feels like I'm a kid again. Even when we crash (and we crash a lot), everyone walks away smiling. It's just such an awesome sensation to fly over and around trees... it's like you are really flying.
You could get a set of Quantum goggles from Hobbyking and modify a Phantom to fly FPV for less than $100 (
http://www.hobbyking.com/hobbyking/store/__53706__Quanum_DIY_FPV_Goggle_Set_with_Monitor_KIT_.html) and then this Video RX/TX set
http://www.hobbyking.com/hobbyking/...Sony_CCD_and_Circular_Polarized_Antennas.html. Then buy a couple dozen props and put it in rate mode and pretend like you are 10 years old and you were granted your wish to fly like a bird.