He is "truly evil". He murders people who can't fight back like it's part of his regular routine of keeping the Imperial fleet shipshape and well-disciplined. He tortures Leia. Even if you think torture is ever justifiable, she is (at that point) a non-combatant, a diplomat. If he was just a little misguided/misunderstood, rather than truly evil, the ending of RotJ wouldn't have half the power it does. It would hardly be a revelation for Vader to turn away from evil if he wasn't actually all that evil. I don't really see what is "badass" about torturing and murdering people who can't fight back. It's a little pathetic, actually. The Force-choking he likes to throw around to put the fear of god in the Imperial officer corps is the natural progression of Anakin's tantrums.