Omega Fighter is easily one of THE most fun shmups ever. Games are fast and furious, but always rewarding!
It manages to combine pure shooting action with slight complexity, and succeed. Unlike games like Galaga, which has only shooting, and a game like Alpha Mission 2, which is super complicated in it's weapon system, Manages to combine the two to create one ultra fun game.
I remember dropping many a 20c piece into this machine as a kid, marveling at the creative Slow-Motion bombs (well before The Matrix made such scenes famous!), and a pumping soundtrack. With the story that's told so effectively through just a few cut scenes, you're battling to save the earth from destruction by an incredible invading space fortress. In fact, each level of the game sees you battling in and around the vast invading ship, strategically taking out key weak-points in an effort to under it's evil plans.