Quite a faster paced action game! Exploring the sewers (who seemed randomly generated?) and fighting the alien rats has a good feel of speed and killing them felt good. I wasn't too sure about the garbage however, I think you end up fighting rats more than anything and there is not a lot of life to spare.
I really like how the more you go down, the more things are added to the pool, either spaceships or purple aliens to add to the mix.
If you end up pushing the idea, I hope you add animations or a way to prepare the player to the attacks of the rats! Right now, I ended up taking a lot more hits than I had hoped.
Congrats on the game!