I remember playing Alien Syndrome with such overwhelming fondness that the nostalgia may taint how effective this review is, but I'll see what I can do.
I still remember thinking how great those crappy 8-bit aliens looked back when I was a kid, using my own imagination to fill in where the pixels left off. Running around on space stations and star ships blasting through an unending army of aliens, while trying to find my way around and rescue the trapped people. You even had the choice of playing as a boy or a girl.
Funny thing is, I didn't own a Master System, and never played one until I bought mine about a year or two ago. This is all thanks to the wonderful efforts of the Tengen Company, who would make illegal ports and unendorsed game and, thanks to their unique cartridges, could release them on the original NES without buying a development kit from Nintendo.
But it IS a Sega Master System game, and one I now own, being the fan I am.
It's a top down game in the style as Smash TV and Total Carnage. You grab different weapons -- like lasers, flamethrowers and the like -- and navigate around to collect the people trapped in the level. Once you've got everyone, you then go fight the 8-bit era's inevitably impossible bosses. Then it's on to the next level, new map, and new aliens.
Alien Syndrome's best feature - the 2 player co-op. What ever happened to that idea? It's not found in NEARLY enough games these days.
Alien Syndrome for the SMS is a classic that I recall fondly. In fact it was probably the most fun I've had on the "Master System," but for those of you who didn't play it, you might as well go out and find one of the other versions.