The platforming part sadly felt a bit unsatisfying, my suggestions for possible improvements would be to either increase gravity slightly to lessen the floaty feeling of jumping, or allow you to control the height of the jump by holding down the spacebar. Other things to think about might be to add some more ground friction to reduce sliding on stops, and it wouldn't hurt to add a tiny grace period when exiting a platform either. (Most 2D platformers give you a few frames after leaving the edge of a platform where you're still able to jump, which gives a solid feel to the controls)
The pause when going into first-person mode is really nice, even if I think it would work better as a strong slow-motion instead, but then again I'm a huge fan of slow-motion in games so I'm a bit partial on that particular area.
I really like the extra puzzle aspect you get from having multiple slices of the world to move in though, and the fact that you can remove enemies between the sections is quite amusing.