I don't know man. You're right that it didn't divide people but that's because Empire at the time was unanimously considered weaker than Star Wars since it wasn't as fun and joyous. Also it was thought that the movie felt incomplete and didn't have a beginning or end. People didn't get upset about the characterizations of say Luke, but they thought the everyone seemed more grumpy. Yoda was considered a technical marvel, and some critics did concede that the movie was well made, but they'd insist it lacked the magic of the first.
Hence the common consensus that the movie was only alright. It's only well after fans saw how the saga competed along with the benefit of vhs did people finally begin to think Empire was better than Star Wars.
But you have to remember Star Wars in 1977 was a phenomenon unlike any other. That was also a self-contained story where, quite honestly no one was thinking about a sequel straight out of the gate. People were still trying to wrap their heads around what they had just seen. That movie revolutionized the industry.
Even when talk popped up of a sequel, it initially was entitled Star Wars II. There were no chapter references suggesting a "bigger" story arc. That honestly became a marketing ploy that has been the potent Kool-aid many still drink to this day. Once Lucas gave it a separate subtitle, then the first Star Wars film adopted it's own subtitle and thus began this episodic journey.
But I have to be honest and say, for me, this new film is just Star Wars VIII. And it feels like it too. So to think that ANY film could reinvent the magic of that first blockbuster is not really putting context to history. You're absolutely right that people were not accustom to a middle section story. That is spot on. But even if it was fully contained with a traditional happy ending it still would not have touched the impact of that first movie.
I saw Empire just like Jaws II, Superman II, Rocky II. We were in that early era where sequels were really only starting to kick in. Prior to the late 70's the only sequels you really saw or thought about as part of a franchise was with the Planet of the Apes films. But it was actually because those films had begun losing their popularity in addition to the television show, which I loved, getting taken off after only 14 episodes that the industry thought the sci-fi market was dead.
That's why when Lucas approached Mego to make the figure line for Star Wars, an unknown property at that point, they passed because they were already eating crow on the unsold figures from the Apes movies and shows. So when Star Wars exploded, Kenner had gotten the license and had to race to get something made. Enter the insane popularity of the 3 3/4 inch figures and the end of the Mego 8 inch era.
So Star Wars changed the face of everything in pop culture. It changed not only the subject matter of what people watched, but how they watched it, and what the kids played with for merchandise. Plus it forever changed how movies were made and marketed. No follow up film was going to match that achievement no matter how it was structured.And they still haven't made one to top it yet either. That's why people like me who were in theaters for that first film hold such reverence to the title, because it was utter magic back in 1977. There was NOTHING like it anywhere. Star Wars was not a movie, it was an event.
When you saw that film, suddenly everything felt possible. Anything that could be imagined suddenly felt obtainable because this movie made something this far out, seem strangely real. It was a neat time to be a kid and ride that wave of wonderment. Today's films at best can only pay homage to it. That's lightening in a bottle we won't see again for a long time. When you say Star Wars to me, there was (and is) only one Star Wars. Everything after that is the subtitle stuff. It will never hold a candle to that first film. And history continues to support that perspective.