They're very awesome :-) I find that I really like the ones with lots of abstract representations and/or have highly intricate structures. (Will put pictures when I have them)
I made my own too, but they weren't very tall or elaborate because the sand is not firm enough. I built a 4-pointed star and a hexagonal-shaped structure and a semi-3D butterfly. ED built a spiral fort and a Greco-style edifice, which looked nice while it was still standing!