The Book Thief by Markus Zusak is indeed one of the best books that I have ever read. Taking place in World War II, narrated by Death itself, it tells the storie of Liesel Meminger, a girl who had to be abandoned by her mother for undisclosed reasons and stays with Rosa and Hans Hubermann.
The novel mostly narrates what happened with Liesel during her stay in Himmel Street (Himmel meaning Heaven). This includes (and is not limited to) making friends, falling in love, hiding a fistfighting Jew, learning the meaning and power of words, indulging in crime, being part of the Hitler Youth, hiding from air raids, and of course, stealing books.
What makes this novel so extraordinary, though, is the way it's narrated. As I mentioned, it's narrated by Death who makes for a charming narrator. Interestingly, he seems pretty human, having feelings, feeling joy and almost crying for a few characters himself. Hell, he gets depressed at points. He has a blackened heart. He possibly hasn't had a vacation since he's started, and his line of work isn't the most joyous. So, he tends to look for distractions, which usually is the color of the sky when every person dies, because for each one there is a different color: red, white, black, breakfast, newspaper.
Interestingly, to give his work meaning, like many humans try to, he collects, the most extroardinary stories he comes across, and Liesel's story is one of those. And that's just the start of what makes the novel so great. The way that Zusak places the story in its context is simply impressive, for you really get the feel of what living in Nazi Germany was like, for the rich and poor alike.
There's also a lot of thought placed into the philosophy of what war really is, and what really happens in a war. Death complains because he gets busy, but he also mentions that when soldiers run to each other, they actually run to him. These thoughts are deep, and this novel is not meant for everyone (treat it like a young-adult to onward sort of story), but everybody should get to read this masterpiece of a novel.