I picked this up because I was looking for an incest-story that wasn't trying to beg for forgiveness. One about real siblings, who had to deal with the guilt and shame et cetera. And while I think that there certainly were stronger, well-executed parts to be found in this story, parts I'm too lazy to talk about (and really, the other reviews here point out the good things well enough imo) the art and story-telling both were lacking:
The characters had little to no expressions, and were generally rather shallow and confusing. The twin-brother stumbled around the same issue again and again, and things that later have been revealed make it harder to see him as a real person. - While struggling with one and the same issue forever is a very realistic trait, it slowed down the plot in a very annoying way, and made it almost impossible for me to find the 'tragic' ending actually tragic. None of the characters made me sympathize. I could understand their motivation, or I could accept where they were coming from, but they never managed to make me 'feel' for them, or to make me care about them.
It wasn't very romantic, nor was it overly disgusting or sick. I wouldn't call it shoujo, either. Sure, the characters were high school students, but they lacked personality apart from their obsessive, possessive and also absurdidly childish love and inability to communicate with eachother like real people sometimes do.
In short: My main problem was that I couldn't trust any of the characters. They lied, they didn't think about the lies (so the reader doesn't really know if they told the truth or not) and their non-existent facial expressions didn't give me a clue, either. That's a little unreliable, and their hot-and-cold attitude didn't make it any better.