I find it fascinating just which characters it gets right, and how the questions lead up to the result if it does. Of course, it's very obvious and logical how it works, but still very cool.
I just tried Prince LaCroix from Vampire Bloodlines. Of course, some of the first questions ("Is he human?", "Is he an animal?") already paved the way, but then out of nowhere the question "Does he rub shoulders with vampires?" baffled me, and from then on it was already pretty clear.
Dexter Morgan was also cool.
"Is the character's name in the title?" - damn.., "Does your character have a sister?" - uh oh, you're getting there.., "Is your character a murderer?" - Dang, got me