I've just been to the cinema to see this and to my surprise enjoyed it as I'm not a fan of the HP films preferring the books.
We watched it in 3D and at times it was amazing, I would go so far as to say it's the best film I've seen in the 3D format.
I took my 6 year old DS and we bumped into a classmate of the same age in the cinema and the boys did not find it scary or sad at all - in fact the part of the film that distressed them both the most was "the kiss" which they both gave a very French "beurk". So if anyone who has younger children was considering but was concerned I'd say go for it.
I can't comment on the language because we watched it in French but I was surprised by how many "merdes" were being flung about so maybe there is some bad language in the English version.