I very much like the idea, but the mountains in the background seem too small, and the tiles change too fast on them. And you cropped! Yay! You should add a fog to the terrain, it'll improve the atmosphere.
Ooo, just noticed the background mountains. I would take a page out of Voids book. Put those mountains waaayy back and make the fog cover them so you see no detail. They will look larger, and will improve your terrain.
First terrain is actually not that bad. I mean, it has its flaws, but I don't feel like pointing them out right this moment. The first terrain reminds me of an old cartoon I used to watch... don't remember its title though.
The angle used in the first one is real nice, but bringing the fog forward will help it greatly as said before. And despite the arches that others don't like, I think they work as a 'building sculpture' hybrid sort of tunnel that may exist in a city entrance.