I've just finished Yumiko's route. It was so so. The first half was bad, but things got better later.
The initial conflict was boring and not very well chosen. Everything was so fast and sudden, I couldn't take it seriously. They didn't refrain from spending time with jokes, but when it came to the conflicts, they brought up in the blink of an eye and finished it quickly.
The romance also started terribly. But the romance got better, specially in the "amusement park" scene. It was indeed, a romantic scene.
The conflict also got better on the second half, aside From the first half, the only thing I liked was the flashback.
I hope the other routes can achieve something higher. When I started playing Grisaia, I expected something as good as Rewrite. I don't think Grisaia can give me some truly masterpiece like Lucia's route, but let's see... Next will be Makina's route.