Nice work! The concept is really interesting and you should surely continue working on this. Just two things to consider in case you do so:
I'm not colour-blind personally, but someone with a colour deficiency might have a hard time differentiating some elements in the game. You could add icons to the cards in addition to the particles and make the red and blue soldiers look a bit different.
Finally, as another user pointed out already, the game really sustains itself, so the player cannot change that much. You could fix this by adding a bit of randomness to the soldiers, with some being stronger / faster /... than others. Then, the player would actually have to make an effort to decide on what cards to play when.
Keep it up!