This reminded me strongly of Flowers for Algernon by Daniel Keyes. That story about a mentally retarded man is a first-person narrative that puts you into an utterly alien mindscape. In this novel it's an autistic English teen: My name is Christopher John Francis Boone. I know all the countries of the world and their capital cities and every prime number up to 7,057.
Also like Keyes book, this novel was filled with the ironies of reading tragedy between the lines to which the narrator is oblivious. Haddon's book uses illustrations, structure, syntax, and other nuances of word-choice to put us into the protagonist's head and heart. The workings of Christopher's mind more than plot is what made this a fascinating read for me. A quick, page-turning read at that and like no other novel I've read, touching and filled with dark humor.
