/jp/ - Otaku Culture

How are the Grisaia games connected to each other?

I read the first two routes (Makina and Amane) and I was completely destroyed by Amane route, especially the ending and the girl camp at Namek. I think I'm going to put the VN down for now and read Bishoujo Mangekyou and probably something else in my backlog to release some steam before getting back to Grisaia.
For when I get back to it, I'd like to know how necessary is it to read every route before moving to Meikyuu. Does it use or expect you to know a lot of information about all the routes or is it stand-alone continuation to the main route? Even if the other girl routes are completely or mostly stand-alone, are they worth reading even in the case I don't really care for the character(s) right now.