Loved it, but really short.
I love the gameplay. It was pretty simplistic, which I like, too many complexities in a Flash game are overwhelming to me and I get bored quickly. However, it was very short. I can see this game going a lot further. I'd love to see more difficult enemies, more power ups and a long gameplay in general.
The those birds that follow you after you are sighted are a great example of how more of the enemies should be. It's okay to have a few easy to kill enemies though to start out.
Other things to change might be fuel for the jet pack and energy/ammo for your weapon. How about a meter that only lasts x seconds while you are flying or shooting that, once it runs out, requires you to wait for it to recharge or to search for more fuel/ammo before you can use your gun or jet pack again. You could also have power-ups, like the health power-ups for the gun and jet pack that extends the meter for longer use.
I think increasing the gameplay length is pretty self explanatory. Perhaps making minor bosses and an end boss.
Good work, I hope there is a sequel!