Sayonara Piano Sonata, or Goodbye Piano Sonata, is in my opinion, one of the most underrated Light Novels that I've ever read. Of course, that's my opinion. If you disagree with it, just... go away. Please.
ANYWAY...
Story -8
It starts off with one of the main characters, Naomi, wandering through a junkyard. There, he meets a girl playing on a piano, who just happens to be a famed piano player who had escaped from her stifling life at home. Naomi helps her with something, and she asks him to forget about her, then just walks away.
The gist of the story is him forming a band with the girl, and a few of his schoolmates, including his childhood friend. The story, while heavily driven by music, also has some great drama. I'll leave it at that and go into it a bit more during the character segment.
Art - It's Light Novel art, which is typically pretty good. The artist did a great job of portraying the characters as well as the instruments they play.
Characters -9
Like I said, the story has some great drama, especially with the developing romance between the protagonist, Naomi, and the girl he met in the junkyard, Mafuyu Ebisawa. There are some very, VERY slight harem aspects, although it's nothing major, and it's only implemented later in the story. The gradual romance between Mafuyu and Naomi was definitely one of my favorite aspects about this read. There's a few side characters, but none of which i want to go into right now.
Enjoyment -10
Yeah, if i haven't made it clear, i love this series. It kind of makes me sad that some of the better Light Novels are incredibly underrated.

Overall -8
There are some minor flaws to the series, but nothing major. At least, noting that should stop you from picking this LN series up. If you think you might like it, give it a try! Unless you're incredibly picky, it won't disappoint.