Aliens Must Die very smooth!
The control was very smooth; though as a physicist I have to say that you're neglecting inertia... once you accelerate in a direction, you would continue to move in that direction until acted upon by an outside force. In plain empty space, there is no friction or anything else to slow you down. (Except asteroids, I guess!) But it's your liberty to have the physics be whatever you want; again, it was very smooth, and it would be a bigger control challenge to be more realistic.
Some complaints:
About a third of the time I wasn't quite sure what the lady co-pilot was saying, so her voice could have been clearer.
When starting waves, having stuff appear right in front of you and getting run into that way isn't fun. (Stuff should come from off-screen at all times, unless you have cloaking/teleporting units.) In addition, it might be nice to have a bigger field of view.
Something about your game's graphics just quite didn't mesh together. Half the stuff (ships, asteroids, the background) tried to look "realistic," and the other half (bullets, the meteors), looked very stylized. I'm a big fan of stylized, so I really liked the way the weapon upgrades looked.
