Where oh where to begin with this one? How about the fact that it takes a lot of guts to set a novel in ancient Gallifrey, during Rassilon's time. There's not a lot to go on from the series there. Then again, when has Doctor Who ever seriously cared about continuity? (Note that I don't say "Doctor Who fandom" there. The fandom has segments that care very very much about it. The series/audios/novels seems to care much less than its fans do.) I believe this is the first time we hear anything at all about how Time Lords are made, not bred, and the levels of creepy that have been the Time Lords throughout history.
Weird and occasionally creepy as the Doctor is (and he is, I have no illusions about that), he is a kind and gentle soul compared to his fellow Time Lords. In this book, we get to find out just how true that is. Even the good guys in this book have issues. The villains are downright execrable. It's hard to find characters to root for in this book, except for Ace and a Time Lord teenager, and even Ace thinks he's annoying. I know we're supposed to want to punch the character of Vael in the teeth, but I think the author may have accomplished this a bit too effectively!
I do like the concept of the Processes. in a way. Evil they are, but they make a strange kind of sense. It helped me to think of them as overgrown, time-traveling bookworms. I think the author could have checked a thesaurus for synonyms for "slime," but that's a nitpick. I can believe that in the Whoniverse there are icky, gunky, gelatin-covered, time-traveling, bitchy, evil intellivores. Sure, why not? It works for me!
The City worked less well. I get that it was supposed to be confusing, but I had a hard time visualizing what it actually looked like. I settled for "big ruin with weird-colored sky." I could never get the feeling for how it was laid out in any way, though, so the buildup to the ending may not have been as effective for me.
One thing that was effective for me was the telepathy. I have always had a weakness for it in stories, and the idea of a planet with no privacy and constant noise was absolutely perfectly realized and made sense. Ditto the reaction of the Scaphe crew to losing that sense. One of the strengths of this novel is that the characters are well-drawn. I may not have cared for the villains, but their motivations were a bit more than generic moustache-twirling. That's worth a lot, especially when, as I said, so many were unlikeable.
Ace is very strong here. She's resourceful and while she does keep wishing for explosives, she has good reason to do so. It's very clear why she's a Companion here; she serves as conscience and backup mind and muscle for the Doctor before he even really realizes he needs it. I liked her. The fragment of potential romance between her and the Time Lord teen is handled delicately for a change, and the reason it can't go anywhere is perfectly handled.
This isn't my favorite novel so far, but it's a good effort.