I feel the most rewarding thing with guitar is improvisation. Whether you just lay down a simple progression and improvise some stuff or if you just improvise over an existing song. It gives you a chance to express yourself.

Its fair enough chugging away on some bar chords for a while, but to really get the most out of your guitar you need to hit those top notes and grab your whammy bar, its a wonderful thing to just sit down and play whatever comes off the top of your head :)