The current keyboard support is kind of unusable. Would be nice to have an option for mouse input to aim and shoot.

This would be also cool for two player games if you have only one controller connected.

Last but not least, how do you exit the game? "esc" only brings you back to the ship screen, but I was only able to exit via alt+f4.

I disagree on the keyboard input. Note how you can combine two keys on the numpad to aim in sixteen different directions.

Mouse aim has been considered and might be implemented along with input options. I would really advise you to find a second controller, though.

Walking out the door (top) exits the game.

Mouse aim has been added, btw, though with a trackpoint in mind.