We'll skip over the disturbing aspect of a brother trying to get it on with his sister, I mean he didn't know and so many jokes have been made about it that I think most people don't even see it as all that weird anymore. But early on in the movie Luke comes across the charred remains of the people who have raised him since infancy. The smoking skeletons are quite visible on screen. The in the Cantina, of course someone loses an arm. Ben fight with Vader takes on an extra poignancy after Revenge of the Sith. He is facing the man he loved too much to kill all those years ago, even after he had slaughtered children. He knows he will probably not be able to bring himself to kill him this time either. So he sacrifices himself, becoming one with the Force so that he can train Luke to do the thing that he cannot bring himself to do. The destruction of Alderaan is something that doesn't really get dealt with in the movie much, but it was the execution of billions of unwitting people with one shot. Leia turns away in grief, and Ben gets shaken when he feels the planet die, then everyone just kind of goes about their business. The next time we see Leia, she is being snarky to Luke, who she thinks is a storm trooper. One thing I loved about Timothy Zahn's Thrawn trilogy of books was that it revisited the huge impact this event had on Leia and others who were off planet at the time. It gae the tragedy some weight that the movie didn't give it. Another dark element of this movie was the interrogation droid. It comes in with it's needles and whatnot, and we see the look of terror on Leia's face, and the door closes so that we don't know what is happening behind it but are left to believe that it is doing more than injecting her with a truth serum, as there would be no reason to cut away dramatically for that.