Nice job on your game! Sadly it seemed a bit bugged for me (I never won the level, even though well over three troops passed), but I stll got a pretty good idea of your game, some comments
-The music didnt stay in one key, which made it very hard to listen too at times, it's great that you make your own music (I've fumbled plenty of time in the department too), in the future perhaps stick to one scale (c major is the easiest) and a more traditional I-V-vi-IV progression, its perhaps basic, but does a good job.
-I liked the simplistic art. Some post processing would've been a cherry on top. You also could've gone for a more stylished colour scheme to further enhance the looks of the game
-There seems to be a weird bug where the troops you spawn go tumbling all over the place
-In general I've seen this idea explored multiple times and it never really seemed to work just like this, I suppose you need some kind of creative solution to create depth apart from just spamming troops with this type of game, I dont have the solutions to this ready at my fingers tip, but its worth thinking about.
Well done on your game, I hope you dont take my criticism too harshly, making games is hard.