Hmm, might have to give this one a try after reading these reviews. I also thought that this book might be a bit light-hearted and comedic, as someone mentioned further back in the thread, but upon learning that it's a lot darker and more psychological than this, I can't help thinking of all of the terrible suffering implied in the Potter books, much of which was excused or given lesser weight through the children's fantasy medium.
And yet I can hardly think of a more vividly terrible backstory than Voldemort's-- a combination of the horrors of poverty, abuse, neglect and resultant childhood trauma creating a man who, in combination with the magical conditions of his birth and the transformation he inflicted on himself before being mature enough to fully digest the consequences, possibly operates within the most tragically constrained conditions of free will in the entire fantasy-villain retinue. He also garners somewhere along on lines of zero sympathy from the other characters, even after they discover all of this, which just adds to how depressing his life story is.
Then of course there is Snape's awful, depressing backstory, Dumbledore's, Sirius', and Harry's own, among many, many others, and basically there isn't a man, woman or child in the entire series who hasn't endured some kind of horrific psychological or physical torture...frankly I don't know why I expect any kind of light fare from Rowling, come to think of it...