I agree that it ended too sudden. As many have already pointed out, the Mangaka probably had to end it sooner as planned, therefore I don't feel that this is a valid critique. But I still feel that after the Touka has died reveal, the Manga drove off a little. Even the newly introduced characters felt a little out of place, since they just barged into the story without a proper introduction. For instance, I have no idea what Maria's purpose is in the story. Is she the doctors lover? Or did she have any connection to Touka? I don't mind having characters with not that much introduction in a one shot, but in a full serialization, I would like to know more about each character.
But that aside, I really enjoyed this manga, especially the first couple of chapters. I also think it covered some interesting points like how to act after a loved one is gone or dealing with an unrequited love. And before knowing what was up with Touka, I was really hyped to know and could not stop reading. So I think this manga did it's job well in giving me a fun time while reading :)