NOTE: There are a few spoilers here, though no absolutely critical ones.
With the Harry Potter series now complete, I want to summarize what I see as its main strengths and weaknesses. The former are, to my mind, well-known. Perhaps the most important is the impressive depth of character development. In addition to the central Trio (Harry, Ron, Hermione), there are numerous secondary characters who develop much greater depths than I would have expected on first encountering them early in the series. Think of cases like Snape, Neville, Luna, Draco, and even Dumbledore (who in Book 7 turns out to be a lot less positive a figure than we have come to expect). A second great strength is the wealth of detail that gives depth and color to J.K. Rowling's imaginary world. Finally, although I don't believe that fiction books should be judged primarily by their ideology "message," I can't help but embrace J.K. Rowling's themes of deep suspicion of government and emphasis on the primacy of universal principles over cultural relativism and chauvinism. Book 7 pushes both of these ideas even farther than previous volumes.
The shortcomings of the series are greatly outweighed by the strengths. Nevertheless, I have two reservations. One is well-expressed by Megan McArdle: Rowling fails to give us a consistent portrayal of the costs and benefits of magic in her fictional world. As a result, the economy of the world she designs has numerous internal contradictions that undermine its believability. As Megan puts it, Rowling fails to explain the "opportunity costs" of magic, as a result of which its not clear why wizards can't just use magic to get almost anything they want:
The low opportunity cost attached to magic spills over into the thoroughly unbelievable wizard economy. Why are the Weasleys poor? Why would any wizard be? Anything they need, except scarce magical objects, can be obtained by ordering a house elf to do it, or casting a spell, or, in a pinch, making objects like dinner, or a house, assemble themselves. Yet the Weasleys are poor not just by wizard standards, but by ours: they lack things like new clothes and textbooks that should be easily obtainable with a few magic words. Why?
Rowling hints at some answers to these questions, and to that extent Megan's critique goes a bit too far. Nonetheless, she is surely on to something.
My second reservation about the Potter series relates to the portrayal of evil. I'm going to save this one for a follow-up post of its own.