This is one of those walk-the-line supernatural/psychological horror stories, a la Henry James or Edgar Allen Poe, in which you can never quite be sure whether ghosts are influencing events, or the protagonist of the piece is psychotic. It's a tough genre to pull off, and Desmond half succeeds - which means he half doesn't. I probably would have liked this book more, if it: a. wasn't so hallucinogenic that it's hard to follow; b. was told in something other than first person, so it wasn't so hard to follow; and c. was clearer on what was going on, so it wasn't so hard to follow. It doesn't help matters any that I'm a jaded reader of this very genre, and recently read Graham Masterton's Trauma, which is very similar but much better written and more effective.
That said, Abandon does at least tell a coherent story, once you go back and re-read a few things and puzzle it out. It meanders a bit, and it becomes fairly clear early on that the protagonist is less influenced by ghosts than he is simply criminally schizophrenic - put more simply, I never believed any ghosts were present (even if some nominal doors are left open for that interpretation), and was far ahead of the surprise plot revelations the whole way.
The greatest problem this book has is that none of its characters are really sympathetic. The most sympathy that can be evinced is for the victims, not because they are likeable (or unlikeable either, for that matter), but simply because they don't deserve to be murdered. None of them are developed enough to have any feelings about, one way or the other - they merely exist as ciphers for the crazed protagonist to deal with. The protagonist (who is never even given a name) tells the entire story in first-person narrative, and is so painfully self-absorbed that an unbiased presentation of the victims wouldn't be possible anyway, even if he bothered to talk about them more.
This would make a good movie, if the plot were presented more comprehensibly. However, the slated upcoming Paramount film sounds actually more confusing than its source material - it turns the protagonist into a woman (Katie Holmes), which, given some of the plot turns of the novel, is going to be problematic at best...though it sounds, from early reports, as if it's all been pretty thoroughly rewritten into a completely different piece, anyway.