Going over the reviews here, Harry Potter superfans have a weird love/hate relationship with this thing. The hate seems to come from comparing it to the book they wish it was, "grownup Harry Potter," heavy on the wonder. What they're missing (I think) is that the lack of wonder is pretty much the whole point. Drop a bunch of actual (if gifted and pointlessly competitive) human beings into Hogwarts (or later, Narnia) and this is pretty much how you could expect them to behave.
As a Potter-indifferent reader I will say the book actually suffers from a surplus of Potter/Narnia/etc. references, many of which I probably did not get. This is probably a better read for ex-fans who've outgrown those books. Those who are still enamored with them will probably find it cynical and depressing, and people who didn't care much about them will find the endless references and in-jokes tedious.