It took me a long time to finish this one. I found each story to be quite engrossing, and so I did them one at a time, often leaving weeks between each playthrough. As such I often found myself forgetting some details, and needing to use the glossary/encyclopedia which the game provides to help you remember its world.
As such my experience may have been different to those who went through it all at once. In summary, I found each story to be very well done, quite compelling, dramatic, and engaging in turns. Each character isvery strong, with only the Loli girl having the weakest storyline, in part because it is the final one and as such delivers all the info that the other 3 storylines only teased at.
This game is very ambitious in its story-telling, and its to its credit that it is able to keep you invested in most of the girls different paths, without bogging you down in its alternate historical setup.
The sex scenes are like most VNs fairly vanilla, and also mostly occur closely together towards the end of a girls route, or even after it. However they work pretty well and there's some creativity amongst the girls.
The music is very high quality, and while a little repetitive at times, the tracks are all very memorable and stick out strongly.
The game's UI is also extremely good, and the extra features provided all add that extra little something to the experience. The game's aforementioned encyclopedia is useful, and its abundance of little extras, including a mini-game, all help round out a very solid experience.
I rate this as a 5/5, because its few weakness are, while fairly common for the genre, not as bad as they could be, and because everything it does do well it does with polish. No corners were cut, and real effort was made to give you the full experience for each girl.
I would personally love to see more VNs that took this path, and found ways to spice up otherwise fairly rote school dramas with higher stakes and mystery, without necessarily getting so epic or hyperbolic as to become pure fantasy or sci-fi.
A definite reccomend.