Gaiman fans will recognise a few things here: in particular, the split between the real world and the supernatural world of the graveyard, and the single-minded hunting of Bod by the man Jack, are respectively reminiscent of London Below, and Mr Croup and Mr Vandemar, from Neverwhere. I think that both are done better in The Graveyard Book - I rewatched Neverwhere quite recently and was a bit underwhelmed. The most obvious creative debt here, however, is not to Gaiman's own previous work but to H.P. Lovecraft: in one memorable chapter, Bod is captured by ghouls and brought to a subterranean world very similar to that of the Kadath stories. Again, I think Gaiman has improved on the original - it is less whimsical, and fits better with the overall worldview of the story.
Diana Wynne Jones blurbs the book as the best Gaiman has ever written, though we must bear in mind that she is occasionally guilty of hyperbole (Coraline does not appear yet to have displaced Alice). While I agree that it has few of the flaws that bothered me about American Gods and Coraline, I still prefer Anansi Boys (which Gaiman withdrew from the Hugo shortlist the year it was up for the award); it is both deeper and funnier. But The Graveyard Book must stand a good chance of winning this year (though I haven't yet tackled Anathem).