Space shooters don't get much simpler than this. There are no real power ups - just fly around and shoot. Game does have warp zones, which is a nice touch. Bonus stages are fun, yet somewhat frustrating. You have to hit all 40 enemies to receive a bonus and their patterns are random. I feel like a bad gamer when I can't hit all 40.
Game holds a special place in my heart as I always played it whenever I entered an arcade as a child. Played it a ton in college as well. Highly recommend this if you're looking for a relaxed shooter game.