One big challenge that pano shares with wide-angle work in general is to build in a sense of visual depth. Unless the shot is thoughtfully composed, wide lenses have a tendency to flatten a scene out... even if it is a dramatic mountain range. Of course, a pano doesn't have to be shot with a wide lens, but that is the norm.

Overall, I have noticed that the panos that I find interesting usually have pronounced foreground and background subjects. This approach can provide useful scale cues and also prevent a scene from looking flat parallel to the lens plane and along the vertical.