kremzike
Max Rebo's roadie
He's saying "How would you, a first time viewer, know when to turn off 6 before seeing Vader turn back to the light?"
*EDIT* Let me elaborate on my order a little. I didn't come up with it. Someone on another board suggested that order a while back when this question came up there, and i totally agreed as soon as I saw it. You start with 4, so all that necessary exposition about the SW Universe's mechanics & mythologies is explained. Luke asks all the questions we need to know and Ben answers them, and it's a nice, contained adventure with a satisfying ending to get you interested in the saga.
Go right into 5 and You get to know the main players better, and you get to know the last of the full-saga important characters in Yoda. It saves the biggest surprise in the saga, and immediately raises the question of how could Darth Vader be Luke's father...
... so you go to an extended flashback sequence of sorts, the PT. Watch 1, 2 & 3 next. You get to understand what happened to Vader and why his redemption is so important right before you watch the film where it happens. Plus, I think that the Leia twin surprise is actually a lot cooler is you learn of it in 3 than in 6. You're gonna guess that Luke is the baby she's carrying, but then you hear "She's carrying twins." What?! So, Luke comes out first, and then the second baby comes out and right before the scene cuts away she names her "Leia". WHAT?! I like that better than Luke's force insight telling him acting as the surprise reveal, and it even makes his sensing it (and her as well) still a nice event in the saga.
Which brings us to 6. You already saw that Vader guy & that good Luke dude, but now you know how tragic Vader is and how Luke needs to save him. Simple OT viewing will do it, but watching the PT beforehand enforces it even more. You saw a glimps of Palpatine in 5, but now you come off of seeing him in his finest hour in 3, so you're well aware of his power & can feel the threat to Luke. You just saw his father turn to the dark side, so you are rooting for Luke to not do the same. You just became attached to Anakin Skywalker, and immediately after you can see him saved. It's just nice. It just works. It's not the only way, but it's a good, creative way.