Lloyd Alexander: The Chronicles of Prydain. All 5 are compelling, but book 4, Taran Wanderer, is a sneaky-wonderful coming-of-age story.
Cressida Cowell: How to Train Your Dragon and its nine sequels. The movie was great, but when I began reading the books to my then-3-year-old, I discovered a different, equally compelling story from that of the movie (both tales get props from me). We eventually read all 10 books together.
Both series are not too long, child-appropriate, and not childish. If your child has contended with Asimov, he/she can handle Alexander and might be able to read Cowell alone.