Re: Star Wars: Knights Of The Old Republic
I've yet to play in a long-term Star Wars game... probably due to poor players, real world events, and the game being set aside for a "test run of this cool new system" which lasted 2 years in real time.
However, I was in a long-term Mechwarrior game that owed a great deal of its success to a strong GM who had a long-term story arc in mind before we started. Biggest pitfall of this system is making sure that the players remember that they are playing a person, not a 'mech.
Also was in a long-running Shadowrun campaign which succeeded because of group of players in love with the genre and some unexpected synergy between the characters.
First off, player interest in the (sub-)genre is absolutely vital. Space Opera, Hard Sci-Fi, Cyberpunk, Anime, etc.... find something that your players can get behind.
Secondary to that is a good, firm grasp of the campaign setting by GM and players alike. Nothing tanks my fun as a player faster than realizing that the character I've designed just doesn't work and that I have to start over.
Keep trying... it will click eventually.