Indeed, the end of the Half-Blood Prince was left out and that was a great pity. The film did have a problem with pacing, with all the "action" at the end. Actually there wasn't too much action in the film.

I really think they wanted to make it a 'calm before the storm'. Too bad, because I never perceived the book that way.

Despite all its faults, I think it is one of the better films in the series, together with The Prisoner of Azkaban.