I'll have to admit this review is a little biased as Peter David is one of my favourite authors, but this is the book that originally introduced me to him.
The story has all the usual things to expect from a Peter David novel - a good A story, a couple of concurrent and standalone B and C plots, well-paced action scenes and some classic comedy moments.
Where The Siege particularly stands out is the fact it's Deep Space Nine's first original novel. David writes a preface explaining why the book ventures into areas the series wouldn't or couldn't at the time, as well as pointing out that at the time of writing, only five episodes had aired, and therefore certain characters might speak out of turn or not be portrayed as the would be in the show.
Compared to the first original novels of other series, The Siege stands up quite well and most of the major characters are all fairly well represented, each with their own unique voice coming through. Even after a decade since the show went off air, the book still holds up well and the characterisation is generally in keeping with the TV counterparts.
As far as pre-"relaunch" novels go, I'd say this one is a rare keeper and a must for any Peter David or DS9 fans, as there's a lot of enjoyment to be had on a number of different levels.