Yes, this game is getting on now (approx 3.5 years old) and uses the veteran Unreal 2.0 engine. But along with Medal of Honor : Airbourne - it's the only FPS game that I've played, completed and repeated several times over.
The key aspect aside from the story, is the brilliant dialogue between you (acting squad leader) and your three squad mates. Named Sev, Fixer and Scorch - each member has their own personality that you can't help but appreciate and sense that genuine feeling of comradery between the four. And while they bicker between themselves, they focus on the job at hand when the shots start firing.
I must have completed this game about five times now and each time I see or hear something that I've missed from before. The knack of the game is to utilise your squad in the best tactical means possible. There maybe a turret further ahead that you can issue a command for one of them to man - but it will do no good if the rest of you aren't there to back him up.
To this day, some of the 'hangar' levels of Republic Commando which see you massively outnumbered against a wave of droid generators - easily make it into my Top 5 of FPS moments. There's just something about the way the game gels when all hell breaks loose. One guy firing from a turret - another behind taking accurate sniper shots and you covering the back of the remaining guy trying desperately to splice the control panel so you can get out of there in one piece.
The game is short in all honesty and is slightly marred by the occasional 'boring' level like the one on the Star Destroyer. But those are minor gripes. What we have here is a great little story of four Commandos, born, taught and raised to act as a four-man unit - planted into a believable and enjoyable FPS game.
Definitely one of the few FPS games in recent years that is absolutely crying out for a sequel.