I haven't read Cartagra yet but I really enjoyed Kara no Shoujo's story, I like sad and deppressing stuff. plus the little parts where the game has you help solve the mystery is a nice touch, makes you feel like you as a player are contributing to the story and not just reading it. I also enjoyed all of the characters in it, which helps. Just don't expect any happy story, and it was even fun getting the bad endings.