On a Pale Horse (Incarnations of Immortality, #1)

Even in a world where magic is an accepted fact, and Satan uses advertising agencies to encourage people to commit sins and go to Hell, the suicidal Zane didn't expect that an actual personification of Death would walk through his door just before he pulled the trigger to shoot himself in the head. Startled, Zane accidentally shot Death, and killed him. In the aftermath of this, Zane discovers that abstract concepts such as Death, as well as Fate, Time, Love and so on, are all represented by human avatars who do the job for a time until circumstances force others to take up their role, and that by slaying the previous Death, Zane has inherited the title. Now Zane is responsible for collecting the souls of those about to die, and judging them to decide whether they go to Heaven, Hell or somewhere else.