I share similar feelings when playing KOTOR, or any game I becoming involved in. When a game is able to invoke those sort of feelings in a player, its a sign of good storytelling. I enjoy games where I feel like part of the story, rather than just a spectator. Ending aside, I felt the Mass Effect series did an excellent job at this too.
When playing KOTOR, I found it difficult to play the dark side. In all the years I've owned the game, I've only played as a full Sith once. Granted, its not like I purposefully chose lightside options 100% of the time, but when making my own choices I usually did the nice thing. I liked being the hero and as silly as it may sound, I felt compassion toward the characters in the game.