IMO one of the worst on an series that is not particularly good. It's 2 and a half hours long with almost not plot. Yes, there's lots of teenage shenanigans and romances that came out of nowhere between characters with next to none chemistry. But as entertaining as that was (and, believe me, it's the high point of the film), they feel rather misplaced in a movie about the imminent destruction of life as we know it. No other scene represents this better than Ginny interrupting a meeting of the Order of the Phoenix to awkwardly shove cupcake into Harry's face. One would assume that after The Dark Lord returned, events would unravel quickly and without mercy, but it seemt that "he-who-must-not-be-named" is in no hurry and need's to take his time destroying the wizardly world so that Hollywood could make more movies.
This film also continues with the tradition started with the previous one of having a plot that doesn't make sense and a macguffin with no use whatsoever. In fact, this movie actually has two: the memory that told Dumbledore that Voldemort made horcruxes (even tough he already knew it), and the potions book that is promptly hidden and had no relevance to the plot. It also features one the weakest revelas of a mystery that no one cared about. Even Harry dismisses the need to know who the Half-Blooded Prince actually was so why are we supposed to be shocked at the reveal that it's actually Snape?