Obsession, I haz it. But it changes constantly. Sometimes I obsess over a television show(Buffy, Firefly...) Sometimes over an idea like moving somewhere, sometimes it is a skill, like crocheting hats.
Lately It has been Harry Potter. I reread all the books, watched all the movies. Then I moved on to fanfic-- The James Potter Series by Lippert--novel length, free, downloads in mobi--and good! Right now I am enthralled with Dumbledore's Army and the Year of Darkness, another fanfic that can be downloaded in mobi. It tells Neville's story back at Hogwarts during Harry Potter and the Deathly Hallows, when Harry, Hermione and Ron are out searching for horcruxes.