All this needs is a little backstory and you're set!

Great game, but maybe just make it more clear what you do, like to tap on the path to move them?
Edit: Nevermind, I'm just stupid. good game, but maybe add a story behind it?

Great game.
Maybe you can add some story to it.

Its a cool game.
One idea which might go against the idea of the puzzle (in which case ignore) but to be able to rotate the game pieces before placing them (or even a limited number of rotations per level) might add an extra little something but its fun puzzle game and makes you think.

Loved it! Slap some more levels per difficulty, perhaps some background story, and that'll be a win!