Hmm, seems kind of like a cross between Tyrian and Pursuit Force.
Really good game, I enjoyed just about everything about it. My only real complaint is that you should be able to strafe by holding down the Shift key (useful for backing up and firing), and also the difficulty and different types of enemies should increase a bit more, the only new additions I noticed to later altitudes were tanks. Perhaps some kind of mobile enemies that try to dodge attacks would have been cool, maybe even some boss battles.
Also, the entire game does feel a little lacking. As others have said, more types of helicopters and items would have given the game lots of variety. As it was, the special was basically a matter of waiting for a bomb, holding onto it for as long as you could, and then clearing the screen. Ejecting was a matter of waiting until you were low on health and then ejecting straight into another helicopter. More variables in the items and helis would have deepened the gameplay.