Number 1 on my list: Divergent storylines. One for Jedi/Republic; one for Sith. I'm fed up with the only real difference to the story being the texture of your face...TSL was the worst in that respect.
Number 2: More customisation options - face, hair, unique robes/capes, sabre hilts, etc.
Number 3: CORUSCANT!!
Number 4: A better ship!
That's all for now...