K On! is about a bunch of girls joining the Keion (easy listening) music club, jam some music, have fun together, and have tea, together, in a cutesy cutesy way. If you are discouraged by this short summary, it is normal and that's sucks. But fear not, once you start watching, it will grows on you.
The characters (Yui, Mio, Ritsu, Tsumugi,...) are all freaking likable because they are all adorable, hilarious and cute. Also their friendship is also adorable to watch, at times, very hilarious. Their journey to conquer their weaknesses are also, very funny. Yep, even character weaknesses are funny to watch.
So, you maybe thinking 'It must be am audience entertainment bait like fan services in those anime with big boobs teenage girls and kawaii lolitas.' Nope. At times they show some passion about music and especially rock, which very based on teenagers reaction when they listen to their favourite genre. It feels very high schoolish. And I couldn't believe how magically it can achieve it, although it does not dwells very deep onto the subject, yeah cup cakes and tea.
Overall I gave it a 9 because I cannot make it a 9.5 and there's not enough music from a easy listening club. Other than that, it's a great anime about friendship, high school, and jamming music.
BTW, those equipment are expensive, especially that Les Paul Yui using. LES F*CKING PAUL, FOR A BEGINNER!!!!! Damn