I like that you had to stop moving to use your shield. I think it would be better if you could only press space to move the player in one direction and use other mechanics to let it do different things. (For example enabling the shield when you are not running.) Because right now it's often hard to to use the spacebar for multiple things.
Design[4/5] Shielding mechanic was great, but using spacebar for moving, turning and jumping is a hassle at times. It was also unclear from the beginning that you needed to keep running through the enemies to pass them.
Theme[5/5] Only one button.
Originality[3/5] There exist a lot of one button games. Would give more if you used the environment more to jump/switch direction.