The Vorkosigan books are excellent. I didn't suggest them earlier because I wouldn't consider them to have particularly big concepts. And for some reason I thought you were looking for fantasy, but I was probably thinking of a different thread.
GGK is one of my favourite authors (top 5) and The Fionavar Tapestry is where it all starts. It does something unexpected in the second book, which had a big impact on me and the way I thought about fantasy and writing in general. It's essential reading before at least one more recent novel.
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