Excellent visuals and audio ! The game feels really good !
The bullet casings flying away are nice but i think they are too visible, i would oftenly mistake a bullet for a casing and vice-versa which made doging difficult in some cases. I found destroying bullets really hard and overall could not get good enough at planning the perfect route despite the markings while shootint at every incoming bullet and guard but still avoid civilians to simply fly through most combat. The civilians were a bit hard to distinguish from guards sometimes, fortunately enough you didn't placed lots of them. Ah also, why is the gold green ? xD
To me the game was really more of a "spot the enemy, go back to a safe zone to fly while preparing the correct aim, stop flying and move back to where i can shoot the guard, if possible off-screen" than an action shooter. I still enjoyed it quite a lot but i'm pretty sure i did not get the experience wanted. I tried to replay the game after finishing it, i was better and could in some occasion fly, bounce and shoot like in the gifs, but i would only really do that at the beginning of the levels. The reason being that defense is way to hard for me to pull off while flying through a danger zone, so it made playing like super risky and most of the time i would die.
Also, since you shoot faster than the guards, and considering the precision needed to destroy bullets, it is actually way easier to aim while hiding then align yourself with a guard and stop moving, wait until your bullets reach the guard and repeat. Trying to move a bit to avoid bullets will most likely make you miss a bullet and get shot, which is also true when flying around, as soon as you're getting shot at by multiple guards at the same time - or also in tight spaces - you're very likely to randomly fly into a bullet.
I had some issues with collisions, corridors of only 1 tile wide made movement and combat hard, using the jetpack inside would almost always result in a weird collision sending you in an undesired direction, making the player's collision box smaller could help but i think not making tight areas would be better, they don't let the player use the cool and satisfying fly and shoot mechanic and actually encourage waiting for the bullets to reach the guards while not moving. The gold bars were sometimes super hard to pick up, or instead get picked from far away. Also sometimes the doors would close before i reached them, they add a nice mechanic but when you get locked up near the end and have to restart it gets very frustrating :x
I still did finished twice the game with all bonus bar though, but if i hadn't played the game safely and pre-aimed most kills i would have never got them all.
Ah one more note : the ability to shoot off-screen guards is really powerful, they don't shoot at you and you can kill them safely, but in some cases this is needed and it shouldn't be, like in the last level on the left side's vertical corridor, not killing the guards prior to seeing them makes it super hard to react in time if you're flying toward them.
Finally : i think your game would benefit hugely from showing a map of the level, not only it fits the heist theme really well, but it would make planning your route so much easier and enjoyable
[Wall of text over] I had a great time playing despite having *some* thins to say, great job !