Let me honest, I am not a die hard Harry Potter fanatic. I have only read the first book, which I found really too cloying to continue with the rest of the series. I am starting to regret that now, however, as both the Deathly Hallows and Half-Blood Prince I have really had trouble following.
Simply put, I think if you haven't read the books, you will be lost trying to follow the plot. I am guessing that the movie is very true to the book, and if you have read the book it will most likely make the movie much more enjoyable. However, the movie itself seems very abrupt as the plot twists and turns throughout the movie, but in the end doesn't really go anywhere.
As at the end of the Half-Blood Prince, Harry has still only located one more of the magical Horcruxes at the end of the movie, leaving him with the seemingly insurmountable task of finding (and destroying) the rest, even though he has no idea where to find any of them. It looks very likely that Part 2 will be an endless series of impossible tasks that make it look as if Harry is going to be doomed, only to have him beat impossible odds at the end and triumph.
Bottom line, I don't think this is a movie you will enjoy if you haven't read the books.