I agree 100% with insanolord on the self defense aspect, always have held that view BUT it is not true they shot similtaneously that was fixed in later versions in the ORIGINAL, I have it on LaserDisc btw, Greedo never gets a shot off he just gets his head blasted and falls to the table. Han shoots at the exact moment he says "I bet you have BLAM Greedo dead. YES Greedo had the gun pointed already but he never got off a shot in the ORIGINAL.
Also go back to the Luke reuniting with his buddy, it doesn't change the story MUCH but it is a different tone to the scene, going in having just lost Obi-Wan and knowing he is about to die puts him in a down mood until Obi-Wan shows up and reminds me to have hope and to trust in the Force. Being reunited with his friend a moment before take off helps explain why he was in such an unusually good mood for a man about to die. It also changes the impact of the guy dieing a few moments later, having no reason to react his expression never made much sense but adding that little touch did alter the story and the moment even if slightly.
Also go back to the Jabba scene, with that removed you do not know anything about why Han is running from Jabba only that he is. That scene explains a lot of back story, if you leave that back story out it is up to the viewer to image it, the back story is different in the books anyways so hence the idea that he can't make up his mind on what is canon because the scene is the same as the novelization if you do not count the novelization as canon then is that scene canon or not? ONLY if you go by the special editions and later if you ONLY go by the theatrical cuts it is not canon. I KNOW all minor details but lets be honest hard core nerds/Star Wars fans DO obsess over the minor details and lets be even more honest, nobody can agree what is actual canon anyways, some people ignore the "official" canon, and the Official canon unofficially keeps changing.