I've only watched the anime to its completion. (The first season only)
I've watched a tiny bit of the visual novel as well, but not enough to have a valid opinion on it.
The anime of Grisaia is a guilty pleasure of mine, although I like tearing into its flaws quite a bit.
Character arcs can be a problem in some cases, but Grisaia's way of handling them just makes everything worse due to it only being 13 episodes.
Similar anime, like Kanon, that also focuses on character arcs, had way more time to flesh out its characters do to its 24 episodes. Obviously, Grisaia didn't really have that much of an opportunity.
Because of its short length, character arcs were almost always very short, only one character having 3 episodes, while the rest got 2 or even 1. The two character arcs that were shoved into 1 episode felt rushed beyond belief, and I haven't even played the visual novel, so I can't even believe how rushed it must feel to the people who have.
But even with the arcs that were 2 episodes long, they still suffered a lot, and could've needed more time.
The only arc that actually succeeded in not being a rushed mess was the 3 episode arc, which was Amane's.
I can imagine the characters being well executed and more lovable in the VN, but in the anime they certainly were not. Or.. At least not well executed, a few of them were still likable to me, especially Michiru.
Sachi, Yumiko, and Makina suffer greatly. Sachi's and Yumiko's suffer from the 1 episode treatment, while Makina's is just... Odd, and even kind of concerning. I found her arc to be incredibly boring, along with her character. Easily the weakest character in my opinion.
Michiru's arc actually started out okay at first, but the last half of her arc just completely ruined it. The ending just completely defies logic, and it honestly made Yuuji unlikable as a character for me until later on.
Basically, to teach Michiru that she should continue to live on... Yuuji decides that it's a perfect idea to BURY HER ALIVE.
She was in there for THREE DAYS. She should have died from lack of oxygen, and if not that, than dehydration, as well as other things that I won't go into details about because it's not pleasant.
And she not only survived for three days, but she was able to get out of the box she was buried in, which doesn't make sense at all considering that there was a lot of dirt on top of her that should have prevented her from opening it.
And guess who was waiting for her when she somehow managed to escape? Yuuji.
He explained her plan to her, saying that he knew she didn't truly want to die, and wanted to test her. He even admitted that he didn't have a plan B if she didn't actually come out of the box though, meaning that he was planning on just leaving her in there to die after those three days. (Which she would have, if this anime were more realistic)
But seriously though, you would think after THREE DAYS, Yuuji would be concerned enough to just drag her out himself, as by then, she would have been very close to death, if not already dead.
And the most baffling part is that Michiru was perfectly okay about being BURIED ALIVE right after she got out. In fact, she was instead GRATEFUL to him, and still has feelings for him anyway.
I am aware that this did help her develop and change her mind about life, but I'd still be upset about being forced into a life-or-death situation if I was her.
There are other ways to convince her that she should continue living instead of BURYING HER ALIVE, but I guess I should just get over this.
Like previously stated, only Amane's arc wasn't completely rushed, and was really the only decent arc except for the first half of Michiru's. Amane's arc pretty much saved the anime from being COMPLETE garbage, and proved that the anime could do a FEW things right, but then just mess up everything else. If only the rest of the arcs were treated in a similar fashion.
I must say that, despite the fact that the whole anime deals with disturbing topics, Amane's was easily the most disturbing and horrifying out of all of them, and it honestly took me a bit to recover after I watched it, as I was asking myself: "What just happened?"
It pretty much covers almost any controversial topic you can think of. In fact, the whole anime does. Of course, I don't mind dark content in anime. In fact, it's a bonus for me, haha.
Another problem that some people may face is the constant panty shots at the beginning of the series.
I usually don't mind panty shots or any other kind of fanservice as long as it doesn't occur during serious scenes and ruin the mood, but, unfortunately, this anime does just that.
Several panty shots will occur during very tense situations, kind of breaking the immersion that I had before.
However, the good thing is that the anime slows down on the panty shots the further the anime goes on, showing them less and less, but it's still a problem that it faces at the beginning of the series.
Before I watched the anime I noticed that many people disliked its rushed pace, and I can totally understand where they're coming from.
The anime is not ALL bad, as there are some redeeming qualities, it's just that the flaws outnumber them.
But despite the many flaws it had, I still found myself being entertained by the series in one way or another, especially during the first few episodes before the arcs officially started, and during Amane's arc.
Long reply, haha.