Really cool result. I enjoyed, playing it :)
It has a cool art style and the flying feels pretty satisfying.
Two small things.. An indicator for your booster could be cool. Maybe a circle around your cursor that fill up to indicate when it is ready again.
And right now i dont know why i should release the left mouse button. ^^ Dont know if it would break the overall feeling, but i think if there is a magazin or some mechanic that forces the player to try to work with its ammo. Or maybe the gun just can overheat if u keep firing.
I had some performance issues. Maybe it is because of browser play, or my hardware. But that should ne something that will easily be improvable with tome optimizing.
Good work :)