Not bad
I thought the game was pretty fun. A save feature would make it better. Upgrades would be good, too. I think the rotating turret really adds something extra to it. It's as much hand-eye coordination as it is timing and plain luck. One thing I would like to see is maybe if you hold the Shift key and press the left mouse button the turret rotates in the opposite direction. Special weapons with the spacebar would be cool, too.
I am not complaining, even if it sounds like I am. With a little improvement this is a game I would come back to again and again.