It's long been my contention that the old Star Wars Expanded Universe was seen by many fans as a way to "fix" the perceived problems of the movies as they aged out of impressionable childhood and into nitpicky adolescence. Reactions to #TheLastJedi have cemented that impression.
The original trilogy was "cool" a lot of the time, but it was also goofy, cutesy, jokey, silly, kiddie—a lot of things that it's hard for a 14-year-old to admit to liking. The EU leaned heavily on the cool—bounty hunters, dark side Force users, brooding—and dropped the goofy.
The EU, and to some degree the prequels, affected the way hardcore Star Wars fans received the movies, allowing them to continue liking Star Wars while growing beyond the pulpy, goofy, fairy-tale parts of the movies. The EU either retconned them outright or let fans elide them.
George killed off Boba Fett, the emblem of "cool" Star Wars, with an accidental death and a burp joke. The EU resurrected him and gave him all the bad boy adventures and backstory an adolescent kid could want. (See: Phasma.)
What little Force training George showed us was pretty woo-woo stuff, all about trusting your feelings and reaching out. What teenage boy wants to think about that? The EU gave them lightsaber forms, Jedi academies, plenty of formal training. (See: Rey is a Mary Sue.) 
George gave us Ewoks; the EU killed them off with the wreckage of the second Death Star. (See: porgs.) George gave us pulpy, overconfident bad guys with questionable tactics; the EU gave us Thrawn. (See: Hux and the First Order chase.)
The movies were filled with pulp SF notions, which is to say technology that's gosh-whiz stuff that doesn't need to be poked at too hard. The EU gave us a backup hyperdrive on the Falcon to explain the trip to Bespin. (See: the "terrible" physics of bombers in space.)
Many of the complaints about #TheLastJedi appear to be coming from people who have conditioned and predicated their enjoyment of IV, V, VI with massive EU injections, as though inoculating themselves against pulp. It leaves them ill-equipped to enjoy movies in the mold of the OT.
We don't get a backstory (or a name) for Palpatine in the originals (see: Snoke), but someone said today "that was a different time. Storytelling has changed." No—storytelling's the same; you've just internalized a zillion EU books and three prequels to allow yourself to like it.
And of course the Luke of the EU was canonized, put on a shelf where he was never allowed to make mistakes, and we've seen how difficult it's been for some hardcore fans to accept a flawed elder Luke. Han shoves Luke into a tauntaun's guts, but milking a critter is "undignified".
The people making the new movies are studying the way George made movies, what he was trying to say, and they're being so faithful to his anti-fanservice pulp aesthetic that they're running into friction with fans of the EU, which was all fanservice and "fixing" George's ideas.
(I don't want to paint with too broad a brush here. Plenty of people, including @pablohidalgo, love both the EU and the new movies. I'm talking about the fans who let the EU nudge them away from what they loved in the OT in the first place.)
I love the original trilogy in large part _because_ of what some people are calling flaws—improbable pulp technology, goofy humor, a Force that resists RPG-style rules, rubber puppets. The new movies going to that well is my jam, but I kinda get why some fans have a hard time.
What some call the "Leia Poppins" scene is the crystallization of my aesthetic—bizarre, beautiful, improbable, unexpected. It's perfectly pulp, perfectly Carrie, a demonstration of the power held by the daughter of Vader—but it's like nails on a chalkboard to the EU aesthetic.
I hope fans rally around #TheLastJedi, the way most of us grew to appreciate The Empire Strikes Back. Time and home video and Episode IX will help. But I suspect that a lot of folks will need to unlearn what they have learned.
It's like the EU set a new set of (pretty limiting) rules about what Star Wars is, and the things that violated them in the OT were only grudgingly grandfathered in. They're acceptable as historical curiosities, but no more of that, please; we've grown up.
Whereas I am all "Give me more of that goofball humor and unjustifiable spaceship design, please! Sign me up for mysticism and porgs!" And I think most audiences are on that side of the line.
