The keyboard + mouse controls were not intuitive at all, and I felt like the mouse guy kept facing the wrong direction when I tried to attack things. Maybe having a bit of knockback to the enemies could help create some space and time to let the player's eyes dart from one side of the screen to the other? Or just somehow have them closer together on the screen so that it's easier to keep them both in view? Either would make it easier to see what's going on and have it be more about skill than about luck and reaction time...
It's a cool idea, though, and with some refinement and lots (and lots) of playtesting, I could see this being a really cool experience!