They're not great books (yes I'll get shit for saying it). Don't spend a lot on them.
The Zahn books were fantastic. The ones after that were kind of 'meh'.
The best Star Wars Expanded Universe stories can be found in the Dark Horse comics.
Mostly true.
Dark Empire I was fantastic.
Dark Empire II was a steaming pile of poached goat balls.
The ongoing series were uneven, but more good than bad.
The advantage that they had was that they were significantly better than the old Marvel ongoing Star Wars series from the mid-80s, which was targeted at 10-year-old boys whose lunch money never made it from the bus to the classroom*. Dark Horse realized those 10-year-olds had all grown up some where along the way and treated them as adults when writing for their audience.
* so basically, Mirth.