I generally like the interior part of an exterior door to be painted same color as the trim, if you are allowed to paint the exterior, you could pick a pretty fun color for that. Of course thats not saying you couldnt paint your door another color. I have seen it done, even though, it isnt a big favorite of mine, others seem to like it.

If you don't mind covering the peep hole, Hang a tall narrow framed mirror on it and call it a day. It's ugliness will be quite reduced.

Nice idea but I have that full door mirror on the front closet (left in picture). We use that one ALL the time (and don't want/need to switch that one out at this time). There's also another decorative mirror in the front entry space so I think I have plenty of mirrors. But your idea makes me wonder about creating a little gallery of low profile frames... though, the door slams every once in a while (as kids go in/out) so that may not be ideal...