I kid a little, but it is a movie with a lot of black contours and desolation, as the trio might be walking through the British version of The Road minus some of the gray-scale photography.
Empire Strikes Back) is the darkest one, but there was a quasi-dark ending to Half-Blood Prince, so it makes more sense that the filmmakers take Rowling's Deathly Hallows and turn it into what it should be: a ripping good apocalypse yarn. It's usually that the mid-point movie (i.e. So it should make some sense that by the time the seventh book has come around that it's coming down to the wire: the big showdown between Harry and the Man-We-Don't-Speak- His-Name, oh, whatever, Voldemort.
As Harry and Ron and Hermoine and everyone else has grown up, so have the audiences with the Potter franchise.