Really cool concept !
I dig the theme of fending off an alien invasion with WW1 era but more style biplanes ^^
The models also look really good, and i like the abundance of effecs for impacts and not to mention these fancy Explosions :O
Controls are pretty smooth as well, and the mouse aiming made it for just spot on precision for both shooting and navigationg through bullet patterns.
Music is also quite cool !
Overall solid entry, great job :)