This was pretty fun! I was pretty bad at it but not as bad as I was at Cowmets.
I like the whole idea and gameplay and I think it will be even better when you finish out the already planned additions. Little details like sound effects etc will make a huge impact on the game.
I wouldn't mind seeing a game mode with more of a progression of levels, almost like a campaign mode where levels start out easy (less debris, aliens, etc) and get progressively more difficult. But I wouldn't say it's something it needs, just an idea.