Finished the game. My route ranking would be: Amane > Michiru > Sachi > Makina > Yumiko.
Story was good. Characters and voice acting were very good. Art and soundtrack are "okay". Soundtrack is definitely the weakest aspect of the VN.
In the end, Grisaia is not a masterpiece, but certainly not as horrible as some claimed it was. I hope Meikyuu can fix its mistakes.
Sachi's route drag too much after what is supposed to be the climax. It would be fine if the next conflict was something stronger, but it isn't... Not to mention the very inconsistent art.
Yumiko's route was the worst imo. The beginning was silly, the CGs were the worst of the whole game and the development of romance was even worse. What saved the route was the second half, that had some good romantic moments and a nice epilogue and resolution.
Really, those two routes you mentioned... My eyes were just filled with that inconsistent art it was tiresome... Those two definitely had potential, but it wasn't well executed.