Essential reading.

This is a very unusual one; essentially, it's mostly told as a series of vignettes of how the various people in this world are affected by both it and by the Doctor's presence. It's ambitious, weird, layered, and basically everything I was hoping to find in the VNAs.

Definitely a difficult read in places though. It feels a bit like Torchwood at its best, except not quite as dark or intense as that series tended to get. Certainly, however, it is a rather bleak vision of a scifi future, told in a manner that doesn't exactly make it an easy read, but a very rewarding one.

One of the most fascinating parts of this book is that it's Andrew Cartmel delivering a very pure version of his vision of the Doctor. And yet, we actually don't see him in the book very much. And when we do see him, he sort of wanders into somebody else's story, and often his presence is bad news for them. Very bad news. He's in full Time's Champion mode here; he will always act in the interest of good, but sometimes that means not being a good person. I feel this take would ripple through the rest of the VNAs, and would rather significantly inform Russell T's take on Christopher Eccleston's Ninth Doctor. Less so the Tenth, much less so Ncuti. I think Moffat had it in mind a bit for both of his incarnations. Especially Capaldi.

This book has two direct sequels later on in the range, Warlock and Warchild, neither of which I have read, but both of which I am eagerly looking forward to.

Recommended background: None, really. You ideally need to be familiar with where Ace is at this point, but let's be honest, if you're reading this book, you've probably got that down pat.
Worthwhile background: Remembrance of the Daleks (season 25), Ghost Light (season 26), The Curse of Fenric (season 26)

In my reviews, particularly of the Virgin New Adventures, I prefer to use a 4-tier system of grading:
Essential reading - If you want to read all the best VNAs, get all the most memorable story arc beats, and generally enjoy the VNAs without having to trudge through the mediocre/bad books, or perhaps even if you just want to pick up a good Doctor Who book with no intention of reading the entire series, look for this rating.
Worthwhile for extensive reading - Not outstanding, but I won't outright tell you to skip it if you want a sense of the VNAs overall. If you're determind to only read the best, skip these, but for a read-through of the series, I wouldn't skip them. They're the worthwhile, good-but-not-amazing books. You'll get a stronger sense of character arcs, story arc beats, and the growth of the VNAs as a range if you read these, but it will also take you a lot longer.
Not recommended - Not very good. If you really want to maximise your experience of the VNAs, you could read this, but it's definitely not advised.
Avoid at all costs - An irredeemable lump of human fecal matter. Do not waste your time with this insult to the franchise.

In addition, I list Recommended background that you may find necessary for understanding the story in full, as well as Extensive background for some additional details you may find interesting.