I used to play this arcade game 20 years ago, or so, where you piloted a space ship and had to battle little Godzilla looking creatures every level. You would fly over them and carpet bomb them or use a variety of weapons and they would shoot stuff at you. The action was side scroller style. Between levels you would navigate through space and buy power ups. You would then choose the next planet you wanted to conquer. This has been driving me crazy, any leads would be awesome. Thanks!