First things first: This is not a romance. This is a story about a girl who loves her sister more than anything and also a thriller. It gets a little macabre. Not gory, but pretty horrible at times.
It's a thriller first and foremost, and that's where it excels. Characterization can be weird and arbitrary in the way people suddenly act illogically in a way that's convenient to the plot, and the author's prone to a lot of half-assed, unearned swipes at redemption for previously evil characters, but ultimately it's not really the point. This is a thriller. And while you have to suspend your disbelief way more often than not, it's not more than most shoujos, and it's worth it, because Andou keeps you on your toes. There is absolutely nothing predictable about this manga - from beginning to end, it engages you completely.
Not to say it's perfect; this manga has very little reread value. After the initial shock, there's usually a lack of substance, resolutions that come far too easy. But it's not quite a disappointing or a regrettable read, either. There's something to be said for a story that's engaging like this, and it definitely handles its twists better than M. Night. It's akin to that really good thriller you catch on TV; maybe it's not worth $12 and a trip to the theater, but it's not time wasted. If you're in the mood for a good mindless thriller, go for it.
