It's alright.
The jumping backflip and catching a gun midair seems too flashy in the beginning, so I suggest "Siryn" checks rounds in the magazine or practices aiming to show she's prepared. The guy with a hammer didn't look like he was smashed hard into the ground that he died, which means his head should move faster to the ground or there are cracks where his head is. I dislike that the protagonist has disconnected feet from her body, but it's acceptable. I don't like that there is no resolution other than it ending when Siryn's shot dead by an enemy she could kill, but that's fine.
Slow motion is good. Movement and weapon recoil appear controlled, sometimes a little slow when it should be fast, but still good for the action. The big guy is eyecatching and presents a worthy challenge. Maybe you can include more bullet grazes or bullet avoiding that force "Siryn" to move. The amount of time words appear for people speaking is better used than most sequences I've seen, as the shortest sentences tend to be seen too long. If anyone else complains, the dialog used could be given an extra half second on screen.
I might get back to you on a formula for calculating this stuff.
I would suggest something about the sound effects being a little flat, but I think other people have a better grasp about that than I do, so listen for them.