This game is surprisingly good and I think it's one of the best of the old "Invaders" style games. Why? Because it's clever and a lot of fun.
Perhaps the "cheesy" theme is a bit overplayed but at least it's original. And the gameplay does away with the typical invader shields, which I consider a plus. The enemy bombs also descend at various angles, not just purely vertical. This means that the game strategy becomes one of avoiding getting hit as well as accurate shooting; and by the way, after each level is completed, there is a scoring bonus based on your percentage of effective shots.
All in all this gives a simple game much more depth than you might expect.
The sound effects are just enough, not overdone and completely ridiculous, but enough to add interest. Of course by today's standards, sound and graphics are primitive, but we don't play these games in the first place if that's what we care about.
I'd actually rate this game 5/5 for what it is, and that's backed up by the fact that I keep playing it over and over.