There is room for improvement.
Now right off the bat I'll admit to not having played the first game. As such, I am not going to critique the story.
One of the things that stood out (negatively I'm afraid) was the ability to endlessly fire your weapon. I literally played through the whole game holding down Z with the second weapon. I'd definitely add clips, or ammo to the next installment to prevent this in the future. I also didn't like the fact you had to move your character to aim, especially in the diagonal directions; it made shooting those pesky sky hunters in the beginning hard to kill.
That said, I did like the fact that the levels dramatically change; I certainly did not expect Carina to hop off her bike and pursue on foot. The enemies followed predictable patterns yet that didn't make them any less of a challenge to defeat / flee. And those icicles; well, I'll just say they caused more than a few deaths.
The art, as you are probably aware, could use a touch, but I can't criticize you on that, because mine is worse. ^_^
I'd give this game a 7, and keep pushing your ActionScript boundaries!!