+1 to Zelazny's take on magic. Didn't realize Changeling was meant to be a trilogy (although that makes a ton more sense in retrospect, too bad it never had a threequel).

I also find his Chronicles of Amber to be an interesting take on Universe building, although the magic system is less formulated (but damn is the whole Pattern/Chaos thing cool).

All of which to say: if you haven't read Zelazny you should, he's a wonderful writer.