But I've already used it in the past since when I started using the stars system. Sometimes anime reach 6 stars while they're going and then drop later. Examples of works which reached six stars: Anohana, Cross Game, Chihayafuru, Hyouka ... it means that the anime is "ten material" and can actually reach an overall rating of 10/10 (kinda rare for me since I give around a 10 per year and not every year), but it's not written in stone.
Even Golden Time reached that score for a few episodes midway, then it collapsed in the second half.
Shigatsu is ten material but I don't know if it will keep it up, personally I think it won't.
Yeah I saw the first episode when it aired and honestly it looked like the kind of show that doesn't sit well with me. Plus I'm tired of having Sakurai Takahiro voicing those kinds of protagonists, sure he's perfect for the role, but since these characters are all alike, at least switch the voice.
Will watch episode 2 to see how low it goes. It's main salvation so far is Itou Kanae, who's nearly (undeservedly) disappeared from the scenes.
As for Nagi no Asu Kara, well I'm aware that it is a well loved show by many so ignore my ramblings on it .
Aside from the comic violence which people have already noted (but it didn't bother me that much), it was pretty much perfect. And anything that reminds me of the greatness that is Nodame Cantabile is a huge plus in my books!