This was very engaging to play! I don't know if anyone said this but the title in the menu doing a wave was pretty nifty.
The enemy design and arcade style of the gameplay works really well and the game pretty much embodies the theme so that's pretty good design work!
It took me an embarrassingly long time to figure out the aliens weren't the threat but the wall around, so the strategy then became how not to knock myself out with my own bullets and still deal with the aliens (especially that dang yellow one).
This is a really strong entry and it makes a really good arcade experience with replay value, I'd be glad to play again.