Whenever NASA sends photos from Mars, the thing that always strikes me is how much it looks like a Doctor Who quarry, just with a bigger horizon. All those years of jokes about the programme being cheap (not to mention the new series avoiding quarries like the (space) plague, bar The Impossible Planet/The Satan Pit) and that's actually what alien planets look like!

More seriously, the other thing that always occurs to me is how difficult it is to get a sense of scale with no known landmarks or items. Are the things in the foreground small rocks quite close or big rocks quite far away? Probably the former, but I've seen Martian photos where it's a lot harder to tell.