There are two endings. Both start with spoiler (click to show/hide)
your character brutally fucking up Darth Vader, like really fucking him up bad. Then you have the choice to go and kill Vader and give into the dark side, and if you do, you then go and get fucked up by the emperor. The emperor kills you and all your friends before turning you into a robo-slave for him. Good ending is if you go attack the emperor where you basically fuck him up as well, then some douche bag 'jedi' tells you not to kill him. Thanks to douche-jedi's nice call there, the emperor kills him and you, but your friends live and start the alliance in your name. This is apparently canon or something also. So basically you were able to defeat the both Vader and the Emperor without breaking a sweat.
The entire story is really stupid and the high point is basically one random fight against spoiler (click to show/hide)
a hologram of Darth Maul.