The Lord of the Rings, J. R. R. Tolkien
I was proud of myself after finishing this. I was at a Catholic school, and we had Bibles, and I remember comparing the hefty sizes of both books and telling people "I've read a book bigger than the Bible."
(They didn't care.)
What can I say about a book I read 15 years ago and of which a hugely popular movie was recently seen by every person in the world? I can't trust my own memory. I think I liked it quite a bit. I remember building sandcastles representing the various cities in the book. I liked the whole logical geography of the whole thing.
I also remember that my dad thought the book was way too big to handle comfortably, so he cut it into its three component books with a kitchen knife, and announced that I should draw some nice new covers for the parts. Whatever... it fell into tatters.