Also my first (fully finished) vn. After reading like 2 routes of Katawa, and skimming through r/vn for a few minutes I stumbled upon recommendations list and thus on this vn.

Grisaia no Kajitsu is a fine piece of novel, which left me with many warm memories, and to this day helps me to survive in this gray (after reading rewrite) world.

To summarize plot, it's a typical harem school slice of life experience, but only at first glance. The game itself is route based, and each route has good/bad endings.
Plot is revolved around a young man who is transferring to a strange Mihama Academy, elite school which services a handful of students (who are all girls thus garem..)
You'd have to learn about past of all characters, and through various choices pick a girl for yourself.

Well, for non spoiler review that's the most basic as it can get.
I can say, that I enjoyed it dearly, and some of the reveals can be shocking. The whole reason why this vn is recommended to previous Katawa readers is because it resolves the same premise - helping and figuring out people with traumatic childhood experiences. You will learn about various reasons why all the students of Mihama are there.

I read grisaia at summer, it maybe took me a week or something, although it is around 30-50 hours, it's totally worth it.

for the final grade, I give it 9 cutting knifes out of 5