Finished this manga some months ago, despite starting to read it in the end of 2010.
Overall, I liked it despite the tone shift in the last volumes (comedy being replaced with loads of drama) and some anti-climax, especially when Junpei and Aya were about of kissing each other or something. I also hated the ending. The story pushed for a Aya ending for a long time. Even Satsuki and Tsukasa thought at some point of the story Aya was the favorite.
I also agree about Kozue and Chinami feeling like "filler characters", especially the former. I don't hate Kozue, but I feel she debuted in the wrong time.
I think a 8/10 is a solid rating for this manga.