I'll judge the titles my style:

Philosopher's Stone: This one's good
Chamber of Secrets: second best
Prisoner of Azkaban: not the best, but still good
Goblet of Fire: WORST, the goblet only made a brief appearance and had almost nothing to do with the main storyline unlike the stone and the chamber, if it was called the Triwizard Tournament or return of Darkness/Voldemort it sounds much better.
Order of the Phoenix: My fave
Half Blood Prince: I never knew she meant Snape. I thought she meant some random new character. Surprise surprise.
Deathly hallows: Grim enough to be terrifying. :rolleyes:

At least the title tells us how grim and violent things will be from now on. I still can't imagine who will be the last sacrifices before Harry and Voldy settle things with each other. preferably Ginny so harry will experience a temporary emotional breakdown and then make the ye olde heroic comeback after loads of thinking JK JK. Maybe Sirius will come back and help too, if he somehow cheated death and came out from beyond the veil in the Department of Mysteries. Any idea when will it be published?