"Alien Soldier" is a very unusual breed of game. We take control of Epsilon-Eagle, a a genetically engineered alien.
Firstly, I've never seen a better-looking Megadrive game - this thing is polished. The art direction is consistent (and although a little dated), it remains one of it's best qualities. Facing off with the many different bosses will just reinforce in the player's mind the great detail and effort that was put into the characterisations.
The game mechanic is quite original too. Instead of the "one-hit-and-you're-dead" mechanism that so many of the games employ, we have a good amount of "Energy", that, when the player collects dropped items, can be re-charged. But not only is your health fractional, so is your weapons' charge.
When beginning a game, the player can select four from a choice of six weapon styles. Essentially, your genetically engineered protagonist carries four guns. You can switch at any time (with a pretty annoying in-game sub-menu system) to any of your weapons. In fact, this will become essential, as each gun has it's own supply of charge, and overcharging the gun sends Epsilon-Eagle to, well, the high-score screen really. (Yes, you've only one life!).
Anyway, this game really is a run-and-gun stand-out, and the continuity throughout the game (one long level filled with many mini-bosses) is either something to embrace or resent. Stick with it though, it's a great challenge.