This is an important dichotomy in order to understand music of the XX century and classical music in general. Many times there is a great simplicity associated with beauty. Some of Beethoven’s most beloved works are simple works, like the piano piece “Fur Elise” or the first movement of the Moonlight Sonata. Bach wrote works of great complexity but the “Air for the G String” has been heard many times in all kinds of settings and arrangements. However, complexity can make a piece more interesting if the listener agrees to commit to unravel the complexity of the piece and to make an effort to understand it..
I find that there is an optimum level of the ratio of simplicity to complexity for each individual. Too much simplicity makes the work boring. Too much complexity makes the work frustrating as the listener feels left out of the game. This is a very basic dichotomy and I think that much of XX century music tended toward the complex and that is the reason that minimalism was able to thrive. People were so tired of complexity that when Phillip Glass appeared on the scene, the door was wide open for a more repetitive, simplistic approach to music making.
So these dichotomies are like swinging pendulums. Sometimes you get complex music, sometimes simple. This phenomenon happened also at the end of the Baroque era and the beginning of the Classical period. The complexity of Johann Sebastian Bach was such that the arrival of Mozart and Haydn, with their “galant style” which consisted mainly of a melody with an accompaniment was very welcome.
But there is another factor involved here, another dichotomy:
