You must choose three troopers from the available stable, which grows with each successful mission - you only start with long shot and spread. Each of the troopers has a different battle specialty, whether it's long-range fire or a spread shot or a shield. There is a serious ribbon if strategy that runs through the proceedings, as you must choose which type of troopers to send into the conflict. Order 66 is more than a shooter, however. Thankfully, the Jedi put up a little more of a fight in the game than they do in the movie. Two or so screens deep into the battle with the droids, the Emperor comes over the air and issues the dreaded Order 66, and your boss battle is a showdown against one of the Jedi.
You control a set of Republic Commandos engaged in battle with the Separatist's droid army.