Harry Potter and the Half-Blood Prince is the 6th in the series. The 6th and 7th books are my least favorites, and this film does not overcome my prejudice against it. I liked it well enough overall, but I've just got problems with the plot. I don't buy Lupin's romantic interest in this one. I think the final scene with Dumbledore lacks the ambivalence I see in Snape in the book. I think the revelation of the identity of the half-blood prince is strangely done, coming out of the blue after the question has been mostly ignored. I love Luna, though. It's directed by David Yates, who also directed the 5th film.
The New York Times is impatient with the franchise. Moria has a mixed review. Variety reviews it here. Roger Ebert likes it: "I admired this Harry Potter. It opens and closes well, and has wondrous art design and cinematography as always, only more so."