The machine gun is basically a waste of a weapon slot. I just run over infantry and it does minimal damage to armor and towers. Also, the game is pretty much impossible on veteran due to the lack of ammo. The controls and game play are fantastic, however.
The problem with the movement is that the mouse is not attached to a particular pixel on the ship. You have to mouse over the entire ship to change directions. This results in an imprecise, laggy feel. Fix that and add an auto-fire and this game is 5 stars. On the plus side, the graphics are simple but great. The upgrades are creative and fun. Finally, the difficulty ramp is about perfect.
Love the game. One bug, creeps keeps getting stuck in my mazes. And while I like the idea of being able to sell towers, I'm concerned that the game may become a juggle festival.