Knights of the Old Republic is THE Star Wars game of all Star Wars games. You don't get the awesome real-time combat of Jedi Knight 2 or 3, but you get an awesome (although a bit cliche'd) story, amazing presentation, and a ton of memorable characters, including Revan himself. HK-47? Awesome. Jolee Bindo? Awesome. Canderous Ordo? Awesome. And let's not forget the cinematic combat! Did you ever see an RPG from that same time period that had melee and lightsaber combat that was so awesome to look at?
Knights of the Old Republic 2 is ALMOST as good as the original, but they didn't have enough time to finish polishing up the game and completing it, since LucasArts pressed them to release the game in time for Christmas the year it was released.
Republic Commando is a superb first-person shooter. It really is an awesome game. But it doesn't match Knights of the Old Republic.
Battlefront II is incredible. When I played as Darth Vader for the first time, I couldn't believe it. I was ACTUALLY mopping the floor with Rebels as the badass himself! And the Dark Times mod made it even better. The Force Unleashed+Battlefront 2=total awesomeness. But again, it cannot quite compare to KotOR.