David Yates, who also directed The Order of the Phoenix, will be at the helm for the remainder of the series. Yates may not be the best director to tackle the series (that would go to Alfonso Cuaron), but he does seem to have a grasp on how to approach the series and has done a good job through two films so far. There is something to be said for consistency of vision as we steam towards the end and they could have done a lot worse than Yates in what has been the first real test of his skills as a big screen director.
Steve Kloves returns to the series as screenwriter after not working on Order of the Phoenix. It is decent screenplay, although some of the lines do not ring true. Perhaps he just needs to get back in the groove as his work has generally been solid. It gets the job done, but I cannot help but feel it could have had a more natural feel.
The Half-Blood Prince has some great visual moments, such as the Death Eater segment at the start of the film, Harry and Dumbledore in the cavern, Harry and Draco in the washroom, and Bellatrix in the Great Hall all stand out as being memorable.
Bottomline. Overall, the series has been solid, if not quite as spectacular as many would like them to be or believe them to be. It is a series to be celebrated for what it is doing and more often than not succeeding at. This entry probably falls somewhere in the middle in terms of quality, although all of them fall pretty close to the other. This definitely something to experience on the big screen, just keep your expectations in check.