I last read
The Verdant Passage
in 1991 (so I was either 15 or 16). As I never got around to reading (beyond the first chapter) the last book in the series, I thought I might make the effort to start the series over again and see what my reaction would be to it some 20+ years later.
Denning does not do an appreciably good job of bringing the strange flora and fauna of Athas to life, or rather he struggles to find meaningful ways to describe but a few of the strange creatures (it helps to have had the original box set for AD&D 2nd Edition that served as an introduction to the world and, for some reason, I seem to have more recall of that than the details from this book). But what he does do is find a way to introduce seven meaningful characters -- not all of whom survive -- who are largely static in their depiction, but in such a way that Denning uses it as an aid to moving the story along. The five major characters are important throughout the series (though at least two don't make it to book five), and Denning's initial depiction of them allows for the subsequent changes and developments to have greater depth.
At the same time, Denning does a decent job of presenting the Dark Sun setting as one that is not going to yield the typical fantasy heroes. This set uses one another (in some instances, owning other characters), are almost always self-interested first (whether they want to admit it or not), and perform their heroic acts more out of desperation than a sense of duty. It is a kind of mature story, and I have a better sense as to why it appealed to adolescent me as much as it did.
Still, this isn't anything approaching high literature. It is an effective beginning to a licensed serial for a Dungeons & Dragons setting. As a diversion, it is fine. I will note that even with the introduction of all the weird (even for fantasy) creatures, Denning keeps the books an easy read. He doesn't do this by dumbing down his language, but rather by not stepping off the path of the story he is telling with needless diversions or extra (needless) background information.
This isn't a book that a would necessarily recommend to people (in part because tastes in fantasy vary even amongst die-hard enthusiasts), but it certainly is more focused than some of the Dragonlance novels of the same era. And it does serve as a fine introduction to the fantasy setting.