I want to point out that the last book I truly bawled over, like I did this one, was Aslan's death in The Lion, The Witch, and The Wardrobe, which I read when I was nine or ten.
Markus Zusak is truly a master, and this book goes beyond all levels of a must-read.
Okay, now, for the less exciting stuff - ratings, because I know it's nice to have a heads up.
This book is definitely meant for upper-grade/mature readers, but that's mainly because of the subject matter. The book is set in Nazi Germany, and some really heavy issues are dealt with. War and death are main themes, and most of the books that the main character reads are pretty dark. There's also a suicide by a supporting character and a refusal to leave home during an air raid but another minor but recurring character. The main character has repeating nightmare's about her brother's death. It took me three nights to start the book because I didn't want to read it after dark, after I'd started the first page, but once I became familiar with the characters, I was fine. Still, a little creepy at first.
Violence - prominent. None of it's EXTREMELY graphic - some pretty gruesome things are mainly mentioned and not described in detail. Air raids, losing limbs/fingers (a supporting character); dead bodies.
Sex - a nonissue, really. A (somewhat detailed) description of a boy forced to strip down to be examined for Hitler's supreme race of Germans, and then later a character thinking about that boy, naked, but only once or twice, and not graphic. No actual sex at all.
Swearing - mild swearing, but mostly in German; a translation is given once or twice, but after that it's just the German version.
Overall - these things should NOT deter you from reading the book. They all fade into the background compared to the beautiful, amazing, wonderful story.