I hardly ever write reviews on here, but this is the best game I have played in a long time.
The art and controls speak for themselves--just fantastic. The game feel is outstanding. But the cherry on top is the rating system. If you try to advance by just passing the levels, you're missing out on the whole game. Forcing the player to use a different strategy to accomplish a specific goal to earn a three-star rating is brilliant.
Level 13 was my favorite. Having to attrit my own supply while fighting the enemy at the same time was a unique challenge. I've never had to do that in a strategy game before.
Overall, please continue making games in this style. As mentioned in the other comments, a multiplayer mode would be awesome.