Byatt

If we're judging fiction based on the 'author actually enlightened me a bit' category, A.S. Byatt probably comes pretty close to the top for contemporary writers. Lots of people read Possession back in the day, which was pretty good, but I preferred the (ultimately) four part series which began with The Virgin in the Garden and ended with A Whistling Woman.

Posting this, I realize I still haven't read The Children's Book, which I should remedy soon.