Mm.. those duplicates made of SG-1 on first season.. they are back. They got too bored sitting on that planet and decided to start doing missions on their own. The other O'Neill was not very good at following orders too.
So, they run in trouble and real SG-1 is called to help them. A little action, some happening. Teal'c's will have their revenge.. all the duplicate ones die. Looks simple.
It is, but there is something else beneath the simple story. First the moment when duplicate Daniel is going to be killed - the way he looks, not letting O'Neill to risk his life to save him. That moment alone was worth the whole episode. Then the duplicate Teal'c taking the revenge on Kornus.. and the way both Carter and O'Neill reacted when their duplicates died.. That kind of emotional episode.