Well, frankly speaking I approached this rather "cautiously". Not that the warnings of gruesome content or dark story stopped me (in fact, it was the contrary), it was just that I didn't know a thing about this VN, never heard of it before what - a week ago or less. Still, after playing through it for days and getting all the endings but the True one, I have to say that this gets my universal approval and acclaim. The story and how it was narrated were both amazing, the characters were likable and even realistic, and while depressing, the plot was truly good.
One thing though that left me quite disturbed was
how the killers were portrayed. I've had my fair share of fictional murderers through manga, anime, movies and the like, but Kusaka and Shinji were both so utterly twisted and deranged that they left me speechless, especially in some scenes. Rokushiki was a madman as well, granted, but he was just a religious fanatic-turned-egomaniac, despite how brutal his crimes were. I'd say that, if Kusaka was the most gruesome of the trio, Shinji was definitely the most mentally deranged and disturbing.
Also, something very depressing
was Tojiko's death. Never saw that coming, and when it came, it hit hard. Toko's fate in the first four endings was also pretty hard to stomach. =\