Sticking specifically to combat/gameplay related things:
The Tab targeting is absolutely terrible. There is no reason at all why when I have something punching me in the face that my Tab target should select something else 30 feet off in the distance. There's also no reason why when I have a mob flagged as a potentially hostile target specifically centered on my screen that the tab targeting should snap to a non-hostile water elemental way off to the side or in the far distance. If they can't make it smarter they should at least make it more configurable so that this sort of thing doesn't happen if you don't want it to.