This is a full, beautiful, and amazing game! Keep it up! These are the games that become things to buy on Steam.
Though without a doubt there is probably things to add because it is by itself probably not enough content for the Steam Store but it is a concept. You should see if there could be maybe upgrades and downgrades for the player, a bigger map and if possible a randomly generated map. maybe you could add online coop where you have to work with others to defeat multiple knights or maybe there is still one knight but all the incoming resources are owned by everyone, or maybe there is a setting to have two or even three knights. I don't know, it isn't my game and all would need testing and work to see how they play out. Nice job!