Really like this game! Can't wait to see what you do next with it! As others suggested I'd focus on reworking the UI layout, maybe add a few more tutorials to help the player understand what to do. It took me a second to understand the gameplay but when I did it was very fun and built my resources :D . Also maybe have the enemies paused while you are building and when you come back have them start a few seconds later. Every time I came back to that world they just swarmed me.