I picked "Sakura no Uta" up because my favourite manga (Aku no Hana) is said to be heavily influenced by it.
I have this mixed impression about this manga.
On the surface, it's old-style manga of 1990s that focus waay too much on comedy with comic-al plot (like the MC's uncle is suddenly a Godfather and at the end the MC became a world's famous artist despite spending his school life as a closet pervert/ secret introvert). I totally couldn't comprehend it at all (maybe my Japanese sucks, that's why).
But at the same time I feel a hidden depth in it. It's almost like Cather in Rye / No Longer Human, with a cynical concept that humans are phoney... et c (which I LOVE). In fact, it proves to a total MIND RAPE. It's certainly a seinen/mature manga. In fact, not surprisingly, it was voted one of the most 'traumatising' manga among Japanese readers.

All in all, it's probably too edgy for me, but since I like edginess. 6/10, maybe?