I'll get straight to ppotential improvements, the distortion Post-Processing is a bit over-done, the jump is very floaty, the rotation of the cube is a good addition but it doesn't fit in, one enemy can shoot me even if I can't see him, this is extremely annoying, another addition to the game could be moving enemies, it really adds, the performance needs a bit of work, and finally, the bullet speed is a bit low, and I guess that's it! Otherwise, the game is great, great graphics, good audio and yeah! But only if you mentioned the brackeys healthbar sprite in the credits of sprites for the submission questions, amazing submission overall!
Edit: I played multiple levels without using the rewind mechanic, it really isn't a big deal in the game