There are many things about it I like, but the main reason is that in an over regulated world where everything has been made too safe, you're on your own, just you and the aircraft and the elements and your own abilities. For some reason I find that totally addictive - even though it often terrifies me. The only other places I can think of where it applies are sailing - and I like that too, mountaineering (never tried), and wandering in wilderness areas (used to do that).
But this may be a rationalisation of what's become an addiction; if I don't fly for a bit, I just gotta get up there!