I really enjoyed this one. The graphic style in this series I liked more than any other (yet), the story is well executed and the soundtrack complemented the atmosphere perfectly instead of just being BGM noise.
As for the True End, it left me with that special gaping void you sometimes feel after reading a good story. Nuff said. Furthermore, the Obsession ending was a brilliant idea, I liked the careful-what-you-wish-for moment, and it really felt like a finger in the face dedicated to anyone expecting a happy end whatsoever. And, yeah, I see the biggest problems I've had with the story were already mentioned here- that children-from-the-same-mother-and-different-fathers-yet-still-identical-twins thing, and Karen's motives which were weak at best, and definitely not enough elaborated upon. If you go for the whodunit approach, give us the juicy details at least. All in all, KnS 2 scores pretty damn high in my book, and I'll be waiting for KnS 3 with bated breath, hoping Tokisaka doesn't die of lung cancer or go to Rokushiki for therapy in the meantime.