I once wondered why I loved classical music the way I do - and then it hit me - it is because of the universal appeal, the musical nuance, the complexity. This is extremely vague, but bear with me. Contrast Liszt's Consolation No.3 in D flat major to any standard Rammstein song. Rammstein is loud, angry, and obnoxious constantly, as is much of modern rock. Really, the only bands that are not are extremely depressed or hopeless artists that make you want to slit your wrists and dye your hair black.
The Classics, on the other hand, are full of complexity and nuance - they go from loud to soft, smooth to agitato, cantabile to allegro maestoso. The music is so rich that one could spend hours analying and studying just a single score - try that with System of a Down or Metallica and you go crazy.
The Classics speak to us all, if we will but listen.