1) Han Solo spends the entire series watching his "dream house in the sky" or a bachelor pad in Cloud City. Now I'm not claiming that I could write great Han Solo dialogue, but I'm pretty sure the words "Dream sky house" should never come out of his mouth.
2) Leia spends the entire series planning her wedding to Han, to the point that it is her main focus over dealing with the bad guys (who are so wildly incompetent anyway that I guess I don't blame her).
3) Acronyms! Acronyms every where! Have you ever wondered what it is like to read a book that looks like it was spelled out by Alphabet soup? If so, check these out!
4) Idiotic use of pre-established lore. Apparently, Darth Vader's glove is a powerful dark side artifact and a symbol of authority among the Empire (my question is which glove as he wore the same kind of glove on both hands). Also, there is a Mount Yoda, because of course there is.
5) This one's funny because I was having a conversation with a friend of mine comparing all the Star Wars books we've read. He said he's read the worst of the worst, and I said "No way dude, I have. The Jedi Prince Series". And he was like "Oh how bad is it?" and I said "Well, The Emperor has a son that is a triclops" and immediately he goes "Okay, you win" lol. But yes, seriously, The Emperor has a son that is a triclops, a trait so well known that a different character is able to assume the mantle of leadership over the Empire because he's a triclops too!
6) As I mentioned earlier, the villains are laughably terrible. They feel like they were written for a Saturday Morning cartoon and are so hammy in their villany that they would probably embarrass Skeletor. Trioculus (yes that's his name, he is the aforementioned pretender to the throne) is such an incompetent derf-wad that he gets frozen in carbonite AND also killed by a droid that is designed to look like Leia, who he planned to marry and make his Queen of the Empire. (Yes, that's real). This joker wanted to be the next Emperor/Darth Vader and he got frozen and eventually killed, and all before the sixth book. Oh there is also Zorba the Hutt, Jabba's daddy who swindles Lando out of Cloud City (probably the only real victory any bad guys get in this series) and also has a braided beard. No seriously, I'm not kidding.

7) Speaking of that, the illustrations inside the books are wonderfully silly. Take a look at some of these:
8- Oh and each book has environmental messages like save the whales, deforestation is bad, all of that stuff. None of it feels in place with Star Wars at all, and it just comes across as a second rate episode of Captain Planet, but it is hilarious to watch them try to shoehorn environmental messages in stories that largely take place in space.