A good novelisation of a great TV story - considered one of the classics and I have to agree.
The overall storyline / plot is quite an interesting one, shades of Dune and the like, quite a few intricacies and threads to it, that weave together well, especially towards the end building towards quite a strong climax, though the book doesn't quite capture it as well as the TV story.
The Doctor is very good in this story, and yes shows some of this issues with being captured / helpless more than other incarnations, but is still quite proactive and shows an immense strength of will here, as well as his normal intelligence and wit.
Peri is a bit more mixed here, due to the nature of what her role becomes in this story - being quite ill at times, and otherwise being somewhat fought over by others, so quite strongly Damsel in Distress, but still manages to show her own independence and strength when the opportunity arises.
The various one off characters are quite a varied cast, some of them being as prominent as the Doctor in the story, though don't detract from him at the same time, but all help contribute to making this story as good as it is.
A memorable regeneration scene at the end as well, calling back to all the companions of the Fifth Doctor's era, as well as the Master, and some interesting new lines for the Sixth, though they help set the stage for what I disliked about the Sixth Doctor.
All round though, a great read.