In my opinion that is the strength of Katawa Shoujo: You go into it expecting a light hearted RomCom from the visuals and the “made by 4chan”, but rather get a deeper view into the psyche of 5 teenagers, which helps you better understand yourself or others.
Shizune’s route was my least favorite one, but only because the way you have to act to be liked by Shizune is the exact opposite of my own character and that’s not the writers fault