I think what it is is that growing up, these movies were already part of our culture and our lives. I remember back in elementary school, back when I was a little spoiled brat, "Luke, I am your father" was a line everyone was familiar with. So what if Vader was Luke's father? Oh yeah, and Luke gets his hand chopped off, Darth kills the Emperor, Vader dies, and Ewoks are adorable. Since the 80's, spoilers for that movie have been commonplace so much that it's almost like if you haven't seen Star Wars before, you already know everything that'll happen, so why even bother?
When watching them this time, though (I skipped "A New Hope", because I wanted to get to the cool Jedi stuff XD ), I tried watching them objectively, like when Luke goes to the Cloud City under the protest of Yoda and Kenobi ("dont go, bad stuff will happen k" "lol no i'll be fine"), I tried to not view it as Luke going to go get totally schooled, but rather he was trying to fight "destiny" all for the sake of his friends. All that stuff about Leia being his sister and Vader his dad, I ignored, and tried to enjoy the movie for what it was. So then finally at the end, much to my shock...I actually got slightly misty-eyed when Vader died. >_>;;; "I have to save you!" "You already have...!" I sometimes forget how cool of movies these were. And though I know those new releases on DVD are technically better with their little touch-ups...I'm glad I have these old VHS's! ^_^
So now I think I'll go find and track down "The Ewok Adventure"! :D That's Star Wars-related, it's gotta be good, right? ^_^