Harry Potter and the Half-Blood Prince

Got it yesterday, finished reading it today. Hated the ending! Hated it!
If you want to read the rest of this post which includes spoilers, highlight text below to read it better.
How could Ms. Rowling kill Dumbledore so soon after the death of Sirius? And after a mission of pure futility? Unless she is planning to make it a fake death (and I sincerely hope she is just as I hope Snape is a double agent within Voldemort's outfit, she seems to be dropping hints on this although it could be me being hopeful), it is just a bit too much. I know she had plans to make the books "darker" as they proceeded but you've got to leave your audience with some hope, some bit of happiness. The ending to HBP left me dissatisfied and sad. The whole book up to that part was good, maybe a little slow then BAM. Slow pace for 80% of it, sudden horrible news, the end. Not a good way to construct a book. I'm not too angry though because obviously this was a "transitional" part of the series. It wouldn't stand on its own but it's necessary to the whole. Transitionals are never satisfying, take "Part 2" of many movie trilogies for example.
Still, I am not left with a pleasant feeling after HBP. I'm not looking forward to the movie on it as I am not looking forward to the coming movie in which Sirius dies.
Harry's break up with Ginny was surprising but makes sense. Ms. Rowling can't turn the threesome into a cutesy coupled-up foursome, not while Voldemort still lives. She has to maintain the theme of friendship between the original three and anything between Ron and Hermione will remain on the back burner until all is resolved, I'm sure.
One last note on the movies and any following books: of course I will see/read them. I'm still a huge fan. I cannot lie.