This series is not hard-core shoujo. If you're a hard-core shoujo fan and have no plans to read anything but that, you can stop reading this review and stop reading the manga. You're not going to get the sappy "high-school" romance that you want.
I have to say, Motomi Kyousuke in this–––she definitely hit her high point. The character development is astounding, both in the main male character (in which it is obvious), and the female main character (where it is masterfully subtle). In its own way, the plot is gripping, allowing the reader to be pulled in by the romantic tension and suspense (from the mystery of her brother) without weighing down the whole story. There are shoujo elements which simply cannot be ignored, preventing a dark overtone. No matter how deep the characters get, I still have a reassurance that this manga will not end badly, nor will it be too morbid.
That said, the general high points of the story are the character development and the main character herself. She is witty and intelligent, making for good dialogue interaction with the male lead. I also consider the plot to be a high point, despite that many have called it "slow." Compared to other shoujo, they are probably right, but if the plot were to move any faster, I think the story would lose so much. It would lose the ability to portray its characters in the proper light and its credibility as a "unique" shoujo.
Some of the lower points of this manga are, in some places, the muddled plot and the art. Now art is subjective thing, but the art in this, unless you prefer this style, is not going to meet anyone's standards of typical, pretty shoujo. I, for one, like this manga-ka's style, but I thought I should point out the roughness of it. The other thing that prevents this series from being a 10 is the confusion surrounding the plot. While most of the time, the manga-ka does a wonderful job at keeping the suspense going without making it too heavy or overdramatic, she fails at the juggling act more than a few times. Sometimes I feel that in order to lighten up the mood, she adds a typical shoujo fluffy scene, but it ends up out of place, rather than a well-executed mockery of shoujo cliches. There is also the cloudiness surrounding each element of the "mystery." I put it in quotes, because it is actually quite predictable by shoujo standards. Each element of the mystery that is unraveled is generally quite lucid, but there are times when I just have to say "What?" as if she just made a mistake in revealing something or didn't tell the readers enough to want to finish reading. Thankfully, this has only happened a few times thus far.
All I can say is, if you're open to shoujo, read it. My only question would be, for how much longer can Motomi Kyousuke keep up the previously mentioned balancing act? After this series ends, I will probably adjust my rating to account for that.