The main problem with the anime is that it's seemingly supposed to be a character driven story: we get quite a bit of internal monologue detailing the emotions, feeling and motives of the various characters. The problem is that the writing is suspect. Characters will often repeat the same thing over and over again in slightly different, or unnecessarily abstract ways. It's as if the writers have a large vocabulary but not enough, or any new, ideas to apply it to.
The characters themselves are pretty one-note. Hanabi is cute and all, but if you asked me what she was like I'd only to be able to repeat the synopsis of the anime back to you. This idea goes back to the 'realism' thing. Most people don't go throughout their daily lives only thinking of the one problem that's plaguing them. Even if there was one person that did that, I think it's highly unlikely that there's an entire group of people around them doing the exact same thing. 'Characters' and 'character development' are often used as a free pass when someone likes something about a character but doesn't know exactly why or how to express it, which is why I'd rather talk about something else than focus on that. But in this case, where the show is being praised for its realism, I must say that characters that don't seem at all like living human persons doesn't strike me as realistic. Give Hanabi a hobby or something, I'm not asking for much.
"But they're unhappy so of course it's realistic."
"But they're unhappy so it's mature."
"But they're unhappy so it's deep."
or
"But they had sex so it's realistic"
etc.
I don't buy it. Making me care about these characters is like 'creating engaging drama 101.' If I don't care about them why should I be shocked by what is going on around them? This creates an emotional gulf where I kind of want to see what's going to happen, but I don't have to worry about any surprises along the way. In a way it's a good thing because it cuts down on stress, but that doesn't help make the anime engaging on any level that isn't superficial.
I did like the visuals and the character designs however. I felt that the visual design and direction was consistent throughout: it was engaging and descriptive enough to keep my eyes happy. This may be the case of the studio dealing with a flawed source, because they got the mood right... but it's a story that wasn't interesting enough, or maybe even just poorly focused.
The last episode contained the most characterization and charm out of any of them. Hell, the ending was way more reasonable than it deserved to be.
About the sex: novel at first, event that's a stretch, but got boring quick. Some people watching were too easily impressed by the 'they kissed in the first episode' thing and that's how they got hooked, I'm guessing.
