What a good looking jam game! Good tutorial, had no issues playing the game right away without getting overwhelmed! Music changes are perfect to reflect the state of the game.
My experience was a funny one: In the fifth invasion or so my some of my critters were not selectable despite being in front of a e.g. tree. I realized at some point that they are if I zoom the camera a little. By then all my other critters were slain but my still working critter was not attacked :D so I kept him leveling untouched and in the end I went for a single kill strike. Unfortunately the enemies had me down in a few secs but yeah... I had fun!