This is one of those many titles that if you played it as a kid, you'll have fond memories of it today. However if this is your first time playing it.....you'll probably find that it seems dated and repetitive.

I just discovered that there are 26 different levels, and if you destroy the mother ship on the final stage you get a "happy ending." Levels 8,16, and 24 are the bonus target levels.

Also there is a hidden continue feature. After you die, if you hold left and down on controller two at the title screen and hit start on controller one, you'll start from the last level you died on.