All in all, an 'ok' conclusion to the series.
I had two gripes with the book, one not so big, the other way more critical.
First, the book did not follow the standard Potter formula, with school being the gel that held everything together. It was far more similar to your classical 'quest' fantasy novels and unfortunately I think it really showed Rowling's weakness as a writer. It was hard to compare the first six books to other works because of the setting but when you remove that you can far more easily put it side by side with other books and see where it falls down.
The far more critical issue with the book was the lack of any real epilogue or 'denument'. After investing seven plus years and 3000 or so pages into a setting and characters the lack of closure really, for lack of a better word, sucked. It was like watching the LOTR movies without the scouring of the Shire or Babylon 5 without season 5. I would like to think that she did this on purpose in order to leave further writing opportunities open to her, but unfortunately I think that is giving her too much credit.
Oh well, it's all over now.
Other then the really weak ending (gripe 2), I would really recommend the series to anyone. I think it was a blast and a load of fun to read.