For an example of the first, check out this photo by frame*. A few rocks, a custom minifig, and that’s it. The composition, however, is very nicely put together. The minifig pose looks well thought out, while the white space and depth of field of the image make for something interesting to view.
As a counterpoint, please check out this creation by Pippo Zane. I spotted this weeks ago, when it was first posted, and never managed to find time to post it. It should not be overlooked, though, as every crevice of this large diorama is crammed with interesting detail. My favorite detail is the twisted column (both of them, really), but that’s just one of many spots of detail that draw the eye. The display is large enough to draw the eye into detail and make the viewer forget the scale of the entire piece.