I'm late to the game so I'll be posting days 1 and 2 on the same day.
This was a tough choice because I also read On the Jellicoe Road and Game of Thrones last year, two books which I absolutely loved, but Before I Fall edged them both out. Oliver's debut just resonated with me. I loved the characters, the writing, and the story. So many tears were shed, but in a good way.
Honorable mention: On the Jellicoe Road and Game of Thrones.