This is the third in the series of books (the others being The Summoning and The Siege) dealing with the impact of the return of the city of Shade to Faerun and the subsequent release of the phaerim (and this review is about the series as a whole as much as this specific book). As such, it deals with some fairly pivotal developments in Faerun, and if you are interested in the D&D Forgotten Realms setting (such as wanting to run a campaign there) you might well want to read this as background material.
On the negative side, Denning isn't the most fantastic writer. Some of his prose is, in places, quite leaden (although some of his battle scenes can, conversely and particularly in the third book, be quite exciting) and some parts of the series can seem to drag a bit (there is a lot of wandering about in Shade in the second book, which doesn't really enthrall). Also, he is rather unfortunate in that he is using characters, like the Chosen of Mystra (inc. Elminster), that are not really his conception (they are Ed Greenwood's) and as such you get the feeling he is "being a bit careful" with them - not really developing them and almost assuming knowledge about them.
In addition, his grasp of the 3E rules is a bit ropey. Now, this should not be a big deal - the plot is much more important than precise attention to the specific rules - but a few things don't feel quite right. For example, the main hero is a sorcerer - restricted spell selection, right? Not in this book, where our hero can learn and copy any spell he sees someone else casting. I guess the 3E rules were new when Denning wrote the series, but even so that did seem, you know, wrong.
On the plus side, his own characters (like Vala and Galaeron) are much better developed than the "prominent personalities". Also, some of the things he comes up with, while not exactly being in the rules, are interesting interpretations. For example, the use of the shadow weave has moral and spiritual implications in this series which are not really mentioned in the rules. His description of some of the spell effects is quite interesting. And, as mentioned before, his handling of action is OK (and gets better as the series progresses). He also visits some interesting areas and so provides descirptions of places like Myth Drannor, Karse, Evereska and so on.
I enjoyed reading this series. It's not amazingly written, but it is OK and, if you like the Realms, it deals with some major events and personalities that could help flesh out your campaign.