I would call this one the best adaptation yet in the series of films, with my only major complaint being that Tom Riddle is oh-so-obviously evil in the flashbacks. There is no way Dumbledore and Slughorn would not have been able to predict what he'd become, if even on a scale of "That guy's not so nice."
So yeah. Prisoner of Azkaban's movie was crap, Goblet of Fire's wasn't so bad if you ask me, Order of the Phoenix's was more crap, but Half-Blood Prince's is satisfactory, which I can say as a loyal fan to the novels and from a "How much would someone new to this series understand all this" point of view.