The only thing I know about this series is that I bought the first volume of the manga long time ago and HATED it. The only reason I bought this was to get the Nana-chan's song (track 11), and it's one of the worst songs I've ever heard in my entire life. If it weren't for the other songs, which are ordinarily good, I'd have given this CD an 'F' grade.
If you're Nana-chan fan, don't even think about buying this. Otherwise, it's ordinarily good, as I said before.