This was my first thought, actually. I discovered them in 7th grade and read them voraciously. I had never heard of Tolkien or LOTR or any of that stuff so I was completely mesmerized by the 'originality' and scope.
The reason I didn't put it, though, was that I tried to re-read them as an adult just found the writing appallingly bad.
This was my exact experience.
My contribution to this thread: Shantaram by Gregory David Roberts.