Right now I'm going through a big Brahms phase. I love the quartets. Such depth, so much going on at once and yet so simple. Ahhhh.
Why I still love Bach, Beethoven, etc: they do the most with the resources they had. They wrote the music equivalent of Elegant Code.
For example, I began playing the Bach Goldberg Variations when I was in high school in the 60's. I played them in concert when I was at the conservatory. I've gone back to them from time to time. There's a new (to me at least) recording by Murray Perahia that I've been listening to. And of course there are the two sets of Glenn Gould recordings. And EVERY TIME I hear or play these pieces, I hear something different.
That, to me, is a GREAT composer.