While this is still at an early stage, I'd recommend thinking carefully about your input scheme. Obviously, I don't know everything that you have planned, but at the moment there's no reason for space to be jump, so I'd recommend using W/Up to be jump. Similarly, your projectile only goes in the direction that you're facing at the same level, so there's no reason for it to be on the mouse - you can't aim, and there's nothing in your game design document to suggest this will be implemented. The mouse input is totally wasted. If W/Up is jump, shoot can become spacebar, or J, or... Something else. As a general rule, if a game expects me to use the mouse, then I expect to be able to aim/manipulate things with the mouse somehow.
The art is nice. Did you do it yourself?