I kind of disagree. One of the things I like about imas is that every idol gets to sing every song besides some special cases. This can lead to unexpected bad and good pairings, things like Yayoi Tori or Mecha Chihaya for example.
And that isn't a bad thing at all. Sometimes you do get unexpected... but a lot of times, you just get expected.
As for the stories, well. I can't give an opinion on them due to my lack of Japanese knowledge, except (very vaguely, mind)
Yukiho's dog befriending subplot.. I'm most curious about Ritsuko, but then, no proper
idol route in iM@S2, and my bias is obvious.
Her post-route commu makes me wonder if she's fell for PC-P, heh. Though her DLC story description + her solo song's name, well, that seems to answer that point well enough.