Princess and I went to see on opening Friday night. The dark theme continues from the get go and doesn't let up except for a couple of brief moments. It's been a few years since I read Deathly Hallows so I'm not sure what details were left out, which means I think they did a good job of hitting the critical parts of the book. Overall, I think the movie was excellent knowing full well that they had to find a dramatic ending and leaving pretty much everything unanswered. There is no way they could have done this book in one movie, so I think the decision to split it up was the right one.
Also, the kids, who are now all young adults, are pretty darn good actors now. Watching some of the earlier movies, the acting was jarring in places, but that was to be expected. I don't recall any "bad" acting moments in this movie.
I am looking forward to the finale.