I really enjoyed HP7-1. Unlike some of the earlier movies (ahem, HP6, anyone?), there was much more emphasis on the actual story and just enough attention paid to the side issue of teenage angst. I didn't find it overly dark, but I probably wouldn't take a very young child (say, under 8 or so).
Most of the deviations from the book made sense to me, again, unlike some of the earlier movies. Although I must say, Hermione wearing perfume while on the run was just silly. Why couldn't Greyback simply smell her human-ness? I'm sure being on the run would provide its own smell-track, iykwim.
Anyway, apart from HP1 - the most "magical" of the movies - this was my favorite by far. Go see it - I'll certainly be back!