Let's start with Denning's "modern Jedi," as Luke refers to the New Jedi Order. I don't like them. They aren't the shining heroes crusading against injustice that Jedi Knights are supposed to be. After their experiences in the war against the Yuuzhan Vong, the Jedi are not defenders of the weak, helpers of the helpless, and maintainers of civilization. Instead, they claim to serve the Force, as its balancers.
To achieve balance, the modern Jedi embrace both the darkness and the light. They accept torture and death for the advancement of Jedi goals. And the Force, as well as their own murky interests, are the only controlling authorities they recognize. The legitimate democratic government of most of the galaxy need not apply.
Can you say, "Sith"?
To Luke Skywalker's credit, he begins to recognize the folly of the Jedi's new path toward the end of the book. I hope this realization motivates him to correct the Jedi's path, because reading about a bunch of rubes who resemble the arrogant, capricious Jedi from
Knights of the Old Republic isn't my idea of fun.
Aside from the problems with Denning's portrayal of the Jedi,
The Joiner King offers a pleasing experience. Denning masterfully crafts a fascinating yet creepy insect society in the form of the Killiks. (Remember the painting Leia acquired in
Tattooine Ghost, named
Killik Twilight?

) And he deftly incorporates elements of the familiar into the insect hives, with the Unu having absorbed the Jedi Raynar Thul, and the Gorog--the Dark Nest--having assimilated two Dark Jedi. The lightsaber fights we all love can, therefore, erupt.
Speaking of "assimilated," the Killiks are similar to
Star Trek's Borg, in that they have a collective consciousness, and they can incorporate beings from other societies into their groupthink. Alien individuals, a.k.a. Joiners, do retain their personalities at some level, though. Luke says Joiners have a "double presence" in their minds, that of the Killik hive and that of the being in question.
One other alien whom Denning includes warrants special mention: Tarfang, the foul-mouthed, quick-tempered smuggler. Who, by the way, is an Ewok.
Anyway,
The Joiner King, which I suppose refers to Raynar Thul, is a worthy addition to the
Star Wars saga. I just hope that, in the next two books of the
Dark Nest triology, the Jedi change their ways.