With me ther ewere only a few SL I didn't enjoy. Interesting is that some mentioned the drama club girl as their favorite, for me she in the beginning was one of the most boring for me, but she does get a lot better halfway through.
I think my favorite were, first the nurse, the way she's always teasing you and all and second Rise, she's just so cute and trying to get off of showbiz and getting to a normal life. I found it incredibly interesting because japanese people give a lot of attention to those idols, even younger, not that famous, as if every one of them counts, so it seems like they put a character that felt like the most improbable to be put in a game and yet she was wonderful.
As the dungeons, my favorite was the one when
Nanako gets kidnapped
The song "Heaven" which keeps playing is so beautiful and sad that I could not wait to see what happened next.