I liked the concept with the red squares that allow you to adjust them wherever you want, changing the feel in the hand and improving the grip on the surfaces where the fingers touch.
I didn't like the fact that the case is made of hard plastic; I would have preferred the surface to be softer so it would be friendlier to the hand and could absorb shocks more easily in case of a fall or collision. I didn't like that at the top and bottom (edge with microphones and USB port) there is no plastic and the device is exposed to impacts and wear. Also, I didn't like that it doesn't come in a dark color—it doesn't look very nice on a black device as there is a strong color contrast—on lighter colored devices it might look better.

Beautiful OnePlus case that is perforated at the back where you put those little red squares. Thin and fits perfectly.