Just a little cramped
I love your drawing style, and the animation is very classical, so you can't go wrong. Not much action in the 6 levels I played, so you could work on that. However, the background colors kept the visuals very pleasing, and you kept adding new enemies. Maybe if the gameplay was sped up a bit each wave it would make it more interesting. And possibly power-ups in the later stages. I also love the metaphorical imagery. "The use of words expressing something other than their literal intention"; that's irony! Seriously, shooting warmachines down with delicate flowers. Fighting for peace is like fucking for virginity. Nice job, put it in my favs.
Oh, and though I like the style, very retro-shooter arcade style, it could be a "little" taller.
And perhaps some really low-volume bgmus.