It's a tricky one for me. I really enjoyed the film, and see it as a beast separate from the book.
It's that feeling that what is significant in the books would not translate well onto the film, and the HBP's identity has little relevance to the film, except in bringing Snape's skills and his signature curse of 'septum sempra' to the attention of the audience.
I would say that you do have to have read the book to properly get what's happening in the film. I don't think it can stand alone in that regard, and maybe there were better ways around that.
I thought a little more of Dumbledore explaining things to Harry (for our benefit) would have been helpful, but I suppose it depends on whether the film makers were thinking along the lines that they had two further films in which to explain the importance of various bits.
I did enjoy it, but perhaps when it stands alongside the last two, we shall be better placed to judge whether it was good enough.