Great game! Getting through all the levels was challenging, yet an enjoyable process.
The gameplay loop is solid enjoyable - getting resources and buying structures to fight against the enemy keeps the player on there toes at all times. I love the different structures you can build as you progress through the levels, keeping each level intriguing and new.
One suggestion is to add sfx to the entities. Sfx adds so much to the satisfaction of a game and for less effort compared to programming a new mechanic. Also, I was having a bug where the slimes mobs at the beginning of the game were moving off the map when no enemies were nearby.
Overall, great job on your game. Keep up the amazing work!