So, I first heard about KS only a few hours ago or so from a post on SKC. I have to admit, after seeing the title and the subject matter I decided to check out the demo based solely on a morbid curiosity, a sort of "I wonder how bad this could be" sort of thing. (I have to wonder how often you guys get that as an initial impression.)
But holy crap, the demo blew me away! The writing, soundtrack, and art are all so far above my expectations. Extremely professional and extremely polished. The characters are very likable and the dialog so far has been excellent; often witty and funny, and always interesting and easy to follow. The main character in particular I found very easy to relate to (although this is likely in part due to having a similar - if far more mild - heart condition myself), and his interactions with the rest of the cast were natural and believable.
As far as actual feedback goes (apart from gushing admiration, that is), I don't have much to say. I found it a bit awkward following Misha/Shizune's conversations sometimes, but a. that might be part of the point (:P) and b. it's not particularly difficult to follow. The only other thing that comes to mind is that it would be nice to be able to put a name and/or comment on the save states, but that could be a limitation with the engine (I'm not particularly knowledgeable about how it all works).
All in all, a very admirable release. Really looking forward to the finished product now, even though I have a ways to go with the demo.