Amazing game! I haven't managed yet to finish it, but I love how you introduced new mechanics - once I had fun with jumping with the basic gun, you are introducing a new gun and a new gravity mechanic. And all the introductions of the mechanics are really well done! I reckon that possibility to have the screen centred all the time might help with aiming and sometimes collisions behave weirdly (at one point I got stuck in a non-gravity effect after respawning).
Still, this is an amazing entry and I love it!