One of the most satisfying experiences I've had is taking common materials and standard tools and making something that flies. I'm not yet a superb UAV pilot, but, for me, the building is more than half the fun.
Tricopter
This thing is a beast: 3 big motors and a big battery make it weigh more than a pound. It took ~80 tiny screws and many hours to put together the frame
Quadcopter
I maintain I was into drones before it was cool. This was one of my first experiences with the field.
Airplanes
Multicopters are neat, but airplanes hold a special place in my heart. Nothing in my mind compares to the soaring grace of even a small foam board airplane that you built yourself.
Model Rockets
As much as multicopters as fixed wing aircraft are fun to fly, the electrifying launch of an E or F motor is something else.
Accidents
As I said above, my piloting skills are a work in progress. I might be a perfectionist, but I've grown okay with slip ups like what caused this.