Clever idea about the limitation. Attractive visuals. The little fluffy creatures are really cute, I get a Tribbles/Pikmin/Lemmings vibe from them.
Sound would be a good addition. Even a little bit of music or sound effects will really liven up your game world.
Also, I feel that there is not quite enough "feedback" during gameplay. A bit of animation on the cards would help to communicate with the player.