Thanks a lot for your feedback! Glad you liked the game; multiplayer is in the plans, but it needs a lot of work to get it right.
I decided to keep the maps colorless in an effort to keep a clean style, but also to reduce the time needed to make maps. The more complex the graphics, the more effort the map design needs; also, a map editor will be available for users, so I want to keep it simple for them.
Thanks again, more stuff will be added soon!