Though the majority of critics enjoyed Star Wars: The Last Jedi, it's clear that the film has caused a significant divide among its fanbase. Many are praising the film for its different kind of humor and bevy of surprises, while others condemn it for the same reasons. The difference in opinion is too great to be dismissed as general squabbling amongst dedicated fans.
In expressing their hate for The Last Jedi, a lot of fans tend to reference the original trilogy, which is something many have been doing since The Force Awakens. Clearly, there's a gap here worth examining a little more closely.
The original trilogy immediately became a fan-favorite series because it brought something completely fresh to theaters. A space opera like this had never been done before, not with Lucas' effects and concepts. The tech and characters appealed to audiences, while the concept of the Force and the Jedi enthralled them. You'll hear stories from older fans about how when Empire Strikes Back was released in theaters, there were lines going around the block, a phenomenon that lasted for weeks.
Before Star Wars, there wasn't a lot of spectacle in filmmaking, but George Lucas' ambitious approach to special effects changed all that. The technical achievements alone made the trilogy worthy of recognition, and it continues to influence filmmakers today.
The narrative aspects of the trilogy were also unique. Prior to A New Hope, mainstream films never really focused on more abstract concepts like the Force. They were grounded in emotions that people were certain to understand, but the Force was different. Borrowing from Taoist philosophy, the Force can be understood as a medium through which anyone can connect to the larger universe. On paper, it sounds pretty wacky, but it worked and was one of the reasons people were so awed by the original trilogy.
The prequels undid nearly all of that. All mysticism surrounding the Force was overshadowed by-- aside from midichlorians-- the tedium of galactic politics and unnecessary drama. You can appreciate the technical innovation in them but other than that, the prequel trilogy couldn't quite capture the magic of its predecessor...or so it would seem. There's a disconnect there, as well. While older fans agreed that the prequels were just not as well made, younger audiences have fond memories of them and embraced them more readily and, much like today, they argued over whether or not those perceived flaws were actually the films' good points.
The prequels also brought more humor to the franchise. Not just the sarcasm that was littered throughout the originals, but the use of irony and slapstick as well. Those were used a lot more conservatively in the originals, but were clearly appreciated for most part by the new generation, even if they still complain about Jar Jar almost twenty years later. It's undeniable that while they weren't necessarily critically successful, the prequels were still unique.
We can see that the difference in opinion may quite likely be a generational thing. Younger people appreciated the new droids and elegant battles, as well as the more contemporary kind of humor in their films, which is why we see it more and more in mainstream cinema. It's a reflection of changes in attitude occurring over the course of forty years.