Vader is a much more complicated character coming from the OT. "Wait, he's evil...but can't bring himself to kill his son? He is devoted to the dark side, yet... he would risk himself to save Luke? Yet he is ruthless and killed all those people. How can he be good?"
The PT just makes him out to be a angsty pussy for 3 films. There ain't nothin' complicated 'bout that. "Wait, he's bitching because his girlfriend can't love him and he's mad at Obi-Wan ... for some reason. Something about holding him back. Back from what? His a good guy yet...boy he turned to the dark side really quick there didn't he. He ain't deep. He's just stupid."