Hm, actually graphics are one of the least things I care about in a VN. I've never encountered a VN that made me tell 'wow this has incredible design'.
Sure, Key works have well-done neat CGs (and terrible sprites...) but they're just rather plain. Nothing much outstanding.
Thus I don't really care about doujin VNs with terrible art such as Higurashi or Tsukihime, it doesn't matter as long as writing, story, music and such follow.
If I had to choose though, Kara no Shoujo has a really good art and a style I like a lot.