but terribly unintuitive

[color=red]but terribly unintuitive — the same downward swipe that gets you into the camera from home acts as a back button everywhere else. Figuring these things out is a frustrating process of trial and error.

what does it mean “but terribly unintuitive”?

It is very unintuitive (it is not easy to understand and use straight away. It takes time to get used to it.)