I have mixed feelings on this novel.  It is easily the best experience I had reading any of the Timewyrm books, but that isn't saying much.  These four books were a tough and slow read compared to pretty much anything Doctor Who I've read before.  Each were like this for different reasons, and in the case of Revelation I found the book a bit dense and meandering, to say the least.  I basically had to force myself through a huge chunk of the middle, and I think that is explicitly because the nature of this story is so vague and esoteric.  Here we travel into the mind of the Doctor, and while there are lots of interesting details to this, I had a very hard time dealing with a story this surreal and untethered to anything resembling reality.  It's hard to have an emotional investment for something kind of just going on entirely in the Doctor's imagination.

Still, this book does have moments.  There's a scene where the Timewyrm has apparently created the embodiment of Death itself, a Grim Reaper that enjoys a dance with the Doctor, killing him in the process.  It's captivating and a little unforgettable, but then it never really comes up again.  Stuff like that are what both works and doesn't work about the book.  The three dead companions - Adric, Sara, and Katarina show up as terrifying demons that haunt the Doctor as figures of guilt.  So a big part of this story becomes about the Doctor reconciling with these things and learning to accept what happened to those he has lost along the way.  That's good, and a part of the novel that really works, but we don't actually end up dealing with the Doctor's feelings much along the way.  It ends up being expressed as Ace freeing a mental picture of the Fifth Doctor, who plants a flower and everything kind of starts to fix itself over time.

There are a ton of other plot points going on here.  Other past incarnations of the Doctor show up, there's a sentient church that gets moved to the moon, and a particularly creepy sequence where a village of people ambush the Doctor, led by a returned Hemmings (a character from the Timewyrm: Exodus novel).  And Ace really gets to shine here.  We delve into her past, contemplate her future, and she digs deep in a way few if any other companions manage to.  Even that rings as a bit flawed, though, as Ace spends a lot of time angry at the Doctor in this novel for reasons that feel forced and unnecessary.  A lot of this stuff I did enjoy, but it felt like a long road to get there with a lot of plot points that took forever to explain themselves.  We don't actually learn we are in the Doctor's head until very near the end of the story, and I think that doesn't help matters as the mystery makes everything we see up until that point feel like a lot of confused nonsense.  All told, I definitely wouldn't recommend the Timewyrm series overall.  Two of the books were outright bad reads and the other two were just barely passable.