This terrain is very... different. I like the third one. It's very abstract. Which is something you usually don't see in terrain. Also, on contrary to what others said, I think you should go ahead and terrain for whatever makes you jolly. Do it for fun, not for platitudes.
Terrains are really abstract and impressive, but its total random and has no use in any kind of map i think (maybe in some kind of weird rpg or minigame)
my comments i dont want to persuade u to make normal terrains, your terrain is simply art xD. U can make map in which players are vistiting and watching weird countries ;]
1.- looks diffrent but i dont understand the idea
2.-background rox is it from hellfire pensula in wow ? bit 2 much towers
3. coool terrain and i think it can have use in rpg, reminds Darlan a bit
4.- the best and it also has use very impressive!
5.-its the same what 2 ? looks painfull to eyes but i would want to visit such place in some kind of map