Yeah, the theme is music, even if it's not serious at all they shouldn't claimed the theme is music. For me it's more a slice of life than a real anime on music. I hope the music will have place in the second season since I wait something more serious when it come to music (ah ..I miss Beck). Well, it's not a bad anime but it's like Suzumiya (second season) style, it's something really mainstream, to attract people more than a interesting anime. This sequel will maybe more focused on music, since they will do concert, no more at school I suppose so I think they could level up or work harder (and serious ! not coming just to eat or drink tea).
As a bonus, take a look at those 2 links : Mio is sensible and "Utan~" can become a killer-hit
Well, it's a wait and see ...