Star Wars: Republic Commando is a prelude to the upcoming Star wars movie, episode III. Don't worry, though, no plot will be ruined. :)
You play 38 (in the game referred to as three-eight), the commander in a squad of 3 other specially raised Storm Troopers, each with thier own skills. Though they all have something they're best at, it wont really matter, they all peform the same.
Commanding your squad is easy and you wont need to pause the game to map it out. Areas that can be interacted with will have a small icon on them that you can target and either use or send a squad mate to go and use. These actions range from demolitions, sniping, anti-armor attacks, splicing (computer hacking), and more.
The game is fun, but at times can be unfair. You'll find that you will run out of alot of ammo in the 2nd campaign and you'll be forced to use the shotgun you pick up, whose lack of range can really hurt you, or the pistol.
Multiplayer is kinda weak. Online play is fun, but the real fun of RC is the squad commanding, which you do not have in multiplayer.