Moon Cresta is the first game I remember playing. I was on Holiday in Jersey and the hotel bar had a cocktail cab of this. It's a pretty cool game.
It had some cool aliens, like the ones in the sreenie. They are joined at first then split when shot. Also, every so often you get to dock with another part of your ship, which inreased your firepower. Like a power up. When your ship was complete you were powerful as heck. Docking wasn't easy, though.
Heres a video of someone playing the snes version on his psp. He sucks though. Considering its one of his fav games he lost a life on level one. The shame.