While most Star Wars games are based on either the prequel movies or the original trilogy, Knights of the Old Republic was set even before Yoda's time. About 4000 years before Darth Vader and Luke Skywalker during the days of the original Republic.
The plot had you playing as a hero who has been accepted to train as a Jedi. You meet up with the skilled Jedi Bastila Shan who was responsible for the end of Darth Revan. However Revan's apprentice and now Sith Lord Darth Malak attempts to conquer the Republic and the Jedi through his search for the Star Forge.
While it takes quite some time to become a Jedi and carry a light-saber, the combat was surprisingly fun. While you could choose the path of Jedi or Sith, you also had members of your party who could be Jedi, Sith, Droids, and even a Wookie.
The story could rival the original trilogy as it was superb. Combine that with an epic quest with so many things to see and do and you have one of the finest RPGs ever made.