Is this game a VN or a sandbox?
Both. It is mostly a VN, but you have some sandbox elements. Basicly, you need to progress on the story, but you do have some map movement to trigger events. But it isn't completly a free map, is more if you're at home, go to room/kitchen/bathroom. If at school, go to class, or roam around the corridors. etc. The events themselves move you around the map. If the story says you're going home, you're going home. If it says you're going to have a party on monday, you'll have the damn party. And so on.
The game is decent and the characters are generally likeable, but be aware the ending is extremely rushed. It doesn't give justice to the rest of the game. It wasn't a masterpiece, but was still pretty enjoyable, it had a good-feel vibe... until that shit ending. There are events somewhat important to the drama on the story that to this very day, you don't know what exactly happened. "A
student went missing and is important for the development of the story? Whatever, in the end no one will care, let it
be missing forever because yes, the bad guys were already
jailed. You still got your girls, the end."