Do you use "files"? Its garbargio on steroids. You can't just open a <insert about 100 file extensions here> file from the files app. Moving files around is cumbersome at best and downright infuriating most of the time. The "sandbox" nature of iOS is simply not intuitive enough to know how things will react when you move and try to open a file in another app. It just sucks so bad.

Furthermore, "sharing" is broken. Does it copy the file? Does it move the file? Am I duplicating this 200mb pdf when I move it to books? How the ____ do I know? There is a dearth of information and I imagine most people, like myself, give up and use it to read before bed or watch a few videos on the couch. I am never going to by another iPad until the OS is useful beyond drawing, creating music or reading.