The story itself is brilliant, however simple. Those of you who know japanese rest assured that the dialogues are greatly crafted and truly credible (unlike many popular series), arguably due to its being josei genre. To put it like this: the story isn't predictable (I thought I knew how it would end about 3 times and all of them I was wrong (though that may say more about my dumbness xD)) but even if it's not predictable, it's not ridiculous either. The writer was clearly very thoughtful about it (the story is ring structured) and the adaptation is very well made.
The art is perhaps the most lacking part of the series, in particular the character design for Ricchan (Ritsuko) was rather displeasing, but most of the rest is very good. The hand animations for the instrument playing are really good (better than Nodame Cantabile, on par with Shigatsu wa Kimi no Uso, though maybe not as fancily adorned) and the fighting scenes were very good too (have in mind that they're not very relevant for much of the series, however, I'd dare to say they're better than Naruto's and many battle anime's).
Sound is great, though as a jazz lover I may be biased about that, but anyway, the seiyuus do a great job bringing out the characters. Bon for example has very dislakeable aand very likeable phases, and the seiyuu transitions flawlessly between them.
I enjoyed this almost like one of my favorite animes and I wouldn't doubt recommending it to anyone up to a josei romance drama.
The overall score: 9.4 (Story 10, Art 8, Sound 9, Character 10, Enjoyment 10)
