Frontline Commando is basically a shooting gallery, you move left/right, duck, and shoot. And that's it.
Amazingly, even though the game is the same formula throughout, each level manages to be somewhat creative, helping to bring the repetitive nature to a minimum.
I'll be honest, there's not much I can say, if you've played a shooting gallery before, you'll know exactly what it's all about. And whilst it's simple fun, it's also a very good looking game, aided with accurate and brilliant controls, and as it's free, there's no reason you shouldn't try it.