I think I've found one of the key reasons why I prefer the old Expanded Universe to the current Star Wars content: Unique types of villains.
More specifically, people who weren't just Evil Force Users With Long Robes And Red Lightsabers. While there were always a few Darth Vader-clones that popped up to fill up space, so many of the Arc Villains were distinct not just in personality, but also how they were dangerous.
Grand Admiral Thrawn was a military tactician, which wasn't the point of any of the main villains in the Original Trilogy. Grand Moff Tarkin was a "Build a bigger superweapon and bludgeon the galaxy into submission" kind of villain, and Vader and the Emperor were mystical dark wizards. This isn't a complaint or criticism, but just pointing out that military tactics were never on display in the films since that wasn't the type of story they were telling. But Thrawn didn't have prophetic powers or Destiny, he had to analyze and plan around what he could learn about his adversaries. It's a different type of fight than Literal Magic. In the original Thrawn Trilogy, Captain Pellaeon frequently internally narrates how different Thrawn's style of leadership was to either Vader or the Emperor (Even if his art-analysis did verge on magic by itself).
Ysanne Isard was a political and/or espionage manipulator, which was even less a point of the Original Trilogy than military tactics were. She took advantage of the realities of actually needing to build a nation out of an underground military movement. With all of the dirty gutter politics, self-serving agendas, and logistics that doom so many revolutionary movements. I'm not as big a fan of her arc as I was when I was younger (I re-read the Rogue Squadron novels a few years ago and the writing quality is not as good as I remember, and Isard's plans frankly don't hold a lot of water), but the concept is still fantastic.
Warlord Zsinj on the surface seems like a merger of Thrawn and Isard -- he's a military commander who specializes in espionage -- but he also has a big focus that neither of them demonstrated: Business. While he still blows stuff up with his giant space ships and is sowing dissent through brainwashing and spycraft, he's simultaneously establishing a galaxy-wide network of completely-legitimate commercial businesses that he owns through untraceable pseudonyms. They fund his campaigns, give him influence on planets outside of his direct control, and allow him to control resources without any of his adversaries even being aware of it.
Even one-shot enemies like the Ssi-ruuk were so unique: They're invading the galaxy because their technology is powered by living souls and they want to harvest all life in the galaxy. That's messed up, and so distinct from the general "Take over the world" motivation of the Empire.
But as time went on, more and more of the enemies were just "Darth Vader Again". Another Jedi who fell to the Dark Side, or another long-lost schism of the Sith who rediscovered mainstream galactic society, or some other thing that is eventually resolved by a one-on-one lightsaber duel and a personal grudge against the Skywalker or Solo families. It definitely felt like they were out of ideas and kept running through the same villains over and over again.
This kicked into high gear after the Prequels came out, and continued in the new continuity after the EU was rebranded as "Legends".
I wish we could go back to the idea that there could be an enemy who wasn't super powerful in the force and consumed by Hatred Of The Jedi. With their own skills, their own methods, and something that makes them more than just another wannabe-Sauron. Pirates who are just pirates, marauding ex-Imperial Warlords who are just marauding ex-Imperial Warlords, and corrupt politicians who are just corrupt politicians, instead of revealing that Palpatine returned (somehow) all over again.
