There’s no wonder left in the Harry Potter universe. We’ve grown used to apparations and apparitions. We’ve run out of people to meet. Things are falling apart. Thus Harry Potter and the Deathly Hallows, Part I, all out of delight, consoles itself with running and fighting and late-adolescent sexual tension.
That isn’t, ipso facto, a bad thing. The film manages its running and fighting and late-adolescent sexual tension perfectly well. It’s just that it isn’t much fun.
Nevertheless, the film works, but mostly because we’ve invested in these characters over the years. Since the picture doesn’t bother to establish its people independently, I can’t imagine a newcomer to the Harry Potter universe getting much out of it.