There are some pieces (eg Chopin, Lizt) that seem very simple and yet are very complex in their playability, but are beautiful. (As an average piano player, they're out of my league).

I once wrote a few bars (as a contemporary music exercise for a course I was doing) that used all 12 tones in a non repeating manner and it had all the requisite parts: motif, development and resolution, and for the task at hand and my musical ability, it was rather 'pretty'. My teacher loved it.