This is a bit of a mixed bag but you've done some good things, let's start with the positives:
1) The core idea is very interesting and quite cool. Being able to rewind and create alternate selves to fight together creates interesting dynamics. This idea has great many potential to be expanded upon such as having a new enemy that can only be attacked from behind, so you use your alternate self to grab all the aggro and basically shoot behind the enemy with your real self. This rewind mechanic can also be used for light puzzle elements etc. I like it!
2) Good controls - not the best but they feel good. The jumping is a bit off and sometimes I get myself stuck/unable to jump up platforms when I think I have.
I think you're off towards a good direction but there were a few essential polish in order to make it shine:
1) No recoil on the pistol makes it a bit iffy. This is noted because I'm unsure of your game direction. If you're trying to take this game towards a high-adrenaline, all-out-guns-out game like DOOM, then by all means keep the lack of recoil for all out bonanzas. But at the current game direction, it feels off and would definitely benefit from recoil.
2) Needs more feedback to the player, I don't know where I'm getting shot from. I don't know if I'm doing damage to the turrets. I don't know if I'm almost dead because sometimes when focusing in on the action, I would just suddenly die and rewind automatically which takes me off a bit too drastically.
Otherwise, pretty good game. If you plan on revisiting this, consider your game direction and develop accordingly - is it going to be a more slow-paced strategic shooter (now that's interesting), or a more fast-paced high-stakes shooter (like explosions everywhere).
Cheerios.