Fantasy Zone (Sega Master System)

It was reasonably popular when it came out, but not so many people remember Fantasy Zone, especially the young'uns it seems.  It was an interesting shoot 'em up in its freedom of movement, and being able to buy upgrades.  Really tough game too, with lots of enemies trying to plow into your ship combined with the fact that one hit would kill you.  There were some pretty intense boss fights to be had here as well.