I’ve only had limited experience with the EU but I’d be surprised if there was anything worse then The Crystal Star. I can also vaguely recall a novel where Luke falls in love with a ghost or something.
Children of the Jedi is a gem and you will not speak ill of it.
I have just read the Wikipedia (yes, wiki) summary of it and its sequels. They include
- Luke falling in love with a ghost living inside a computer, who later gains a body
- A big cylindrical superweapon called the “Darksaber”
- Luke fighting the same Wampa from ESB, and its friends