This game is fun. I love the idea of having to kill enemies by chucking crates at them! That makes for some very interesting gameplay. I do have a few criticisms though.
I like the art style for the levels, but the player and the aliens don't really match it.
The movement feels a bit clunky, and sometimes trying to move diagonally makes the player stop (but that might just be a problem with the browser, I don't know)
Sometimes the aliens die just by walking into a crate, even if the crate is moving very slowly or not moving at all.
The lighting is cool, I like how all the crates and walls cast shadows, but it would be even better if anything that was in the darkness was hidden. You can still see the aliens and the crates even if they are behind a wall and in a shadow.
Overall, this game is really fun! And that's the most important thing.