The 'Dark Nest' trilogy is often considered among the worst. The storylines were a bit of a mess, and it deviated too much from the core themes and feel of Star Wars. It introduced some elements that were hard to swallow for many fans, like some of the new and rather strange alien species and their behaviors.
In my opinion, 'The New Rebellion' is not a great addition to the EU novels. The story lacks the usual excitement of Star Wars. The conflict seems forced and the resolution is rather anticlimactic. It also doesn't do a great job of building on the existing relationships between the main characters.
Well, 'The Crystal Star' is often regarded as one of the worst. It's got a plot that's all over the place. There are these strange alien concepts that don't seem to blend well with the rest of the Star Wars elements. It's like the author was trying to be too creative and ended up making a mess. The characters also don't act in ways that we've come to expect from them in the Star Wars universe.
The 'Courtship of Princess Leia' is often regarded as a not - so - great EU story. It had a really strange premise. Han and Leia's relationship took a very odd turn in this story, and it felt forced. The whole idea of other species vying for Leia's hand in marriage in such a cheesy way didn't sit well with the overall tone of the Star Wars saga.
The 'X - Wing Series' is among the top Star Wars EU stories. It focused on the pilots in the Rebel Alliance. It was full of exciting space battles and great character development for the pilots. Another good one is 'Darth Bane Trilogy'. It explored the origin of the 'Rule of Two' for the Sith, which is a very important concept in the Star Wars lore.
One of the best is 'Thrawn Trilogy'. It brought back the beloved Star Wars universe in a new and exciting way after the movies. Grand Admiral Thrawn was a great villain, his tactical genius made for some really engaging storylines.
One of the stupidest could be some of the really out - there Force - related concepts that were hard to swallow. For example, some stories had the Force being used in ways that seemed to break the established lore. It was like they were just making up crazy stuff for the sake of having something new.
In my opinion, 'The Thrawn Trilogy' is very important. As I mentioned before, 'Heir to the Empire' starts it off. These novels were really the first to expand the Star Wars universe after the movies and had a huge impact on how fans saw the post - ROTJ galaxy. Thrawn was a brilliant villain, not just a brute force bad guy but a strategic mastermind.
The prequel trilogy has its detractors who think it's part of the worst Star Wars stories. The overly complicated trade disputes in Episode I as a starting point for the whole saga seemed dull. Also, the wooden acting in parts of the prequels and some of the less - than - impressive CGI, like Jar Jar Binks, made it a bit of a let - down for many fans who had high hopes based on the original trilogy.
Some Star Wars EU fanfiction focuses on alternate timelines. Like what if Anakin Skywalker didn't turn to the dark side? This could lead to a completely different story arc, with the Jedi Order remaining strong and the Sith being defeated much earlier, changing the face of the galaxy forever.
Some of the best Star Wars EU novels include 'Heir to the Empire' by Timothy Zahn. It really expanded the Star Wars universe post the original trilogy and introduced great new characters like Grand Admiral Thrawn. His strategic mind and the way he outmaneuvered the New Republic made for a gripping read.