The things that i liked about KotOR was in the following order:
1) The Storyline, it gave that epic feel back to the star wars universe, something which the prequels lacked.
2) The voiceacting and dialogue, it was the first game, movie or book for that matter where i actually cared for the characters, excellent job by Bioware.
3) The music, Jeremy Soule did a very good job on making a collage of his own and John Williams music to this 90 minute long soundtrack. Tracks like "The Sith", "The Sith academy", "Dantooine outback", "Jedi Academy", "Ahto City", "The unknown world", "Boarding the Star Forge" and "Bastila Shan" are on my winamp-playlist and listened to almost daily.