The characters. Seriously, I put the game up for a while as I worked like crazy in another fandom, and got around to reinstalling it.
I forgot how much I adored Mission's good cheer and kind nature. I forgot how much I wanted to pull Juhani into a hug when she surrenders at the grove. I forgot how poetic Canderous was capable of being, and how Carth was really an honest, decent guy once he pulled his act together. I forgot how brittle Bastila truly was, and Vrook's gruff demeanor (though I heckled the screen with "Hey, I'm not gonna be the death of you - that's the OTHER GUY!")
It is a good, solid story. Classically Star Wars in in every sense of the word - epic scope, high adventure, pathos, romance, and humor. I forgot how much I missed it.