Ikari Warriors is a conversion of a rather old coin-op from SNK Corp, makers of the Neo-Geo arcade/home console system. The original coin-op is even harder to find than other systems of the same vintage, because it used rare rotary joysticks (twisting the handle aims your character's gun/grenade arm). Without the special joysticks, the game is unplayable, and these sorts of special joysticks have a regrettably short lifespan. It is often a complaint amongst arcade operators that SNK equipment is of low reliability.
The story appears to be set in Vietnam - up to two players simultaneously stroll about a vertically-scrolling jungle warfare scene, fighting hordes of blue and red soldiers on foot and in tanks, and destroying various enemy installations. Because the ST lacks special joysticks, the control system is a little clumsy, but then the original system was also clumsy. The graphics are quite detailed (and almost the same as the original coin-op), and the scrolling is smooth.
Apart from that, there isn't really a lot to say about this game. The coin-op was never fantastically popular, but all the conversions I've played (Amiga, ST, ZX Spectrum, C64) are quite good.
Verdict: Faithful conversion of the coin-op, although the control method is unavoidably very different. Worth a look, particularly since the original board is impossibly rare. The small play area is excusable because the original game used a vertical monitor; to get the correct aspect ratio on the ST's monitor, you need to reduce the width.