I found that playing though the game as Lightsided Sith was far more rewarding from a moral standpoint then many of the other classes. Besides the SI, whose story I didn't really find interesting at all, all the other classes fit with being light side because only the SW and SI really practice the dark side of the force.
Being a Sith Warrior and picking lightside choices, you feel like a mercyful god stalking the land rather then a "Oh my god, I will kill everyone that so much as looks at me" type feeling when you play darkside.
And what truly makes it interesting, is that we have all seen and read story's of the good guy turned bad, or the evil person being evil, but this has to be the first real instance I have experienced where I use dark side powers, and yet I break the mold by being somewhat good.
The turning point that really made me love the Light side Warrior was after finishing a part of your story quest where you help some republic soldiers, one of them says as you walk away, "Goodbye Sith, and thank you for saving my life". Easily the most profound moment for me in the game.