Really cool game, didn't have any friends on hand but it seems like it'd be a lot of fun to play coop with one! I appreciate that you made it playable singleplayer at all with the divided keyboard controls!
One addition I think would benefit your game is enemy health bars, it's a small thing but being able to keep track of their hp would be a nice qol feature.
Love the gimmick of your actions affecting what happens on your friend's side, that's an awesome idea!