Wow if this is really your first game this is great, my first game didn’t play close to that! So first to the things I would suggest that I would try to improve in an update or the next game:
More clean Graphics would improve your game or at list make the textures Higher Resolution
The player Interface doesn’t seems to scale with the resolution but I would wait also for the other feedback maybe its only on my pc.
The learning Curve is a bit to hard I think maybe make the start level with a bit more health and one or two ammo more.
Some of your assets seems to fly in the first level.
The Controls fell great
The Sound effects are good
Love the overall game concept with the Jetpacks
Sorry if this Feedback is sounding wherry negative but, remember its complaining on a high level I think for your first game and a deadline of 12h you made a great job!