Hmm .. .disappointing overall I think. Don't get me wrong, there were elements that I enjoyed in this story. The Doctor is on his own, so no companions to distract from the `Doctor'iness of the story (if I can put it like that). But overall, I was left feeling that something wasn't altogether right.
The book starts abruptly - there is never, unless I blinked and missed it, any exposition as to how the Doctor knew about this planet and the potentially destructive Fortress and still active weapon. There is never any justification for his having turned up there, nor any reason for him to think, as he obviously does, that nobody else will be there.
I really really could not like Alsa, who plays such a part in the story - I'd prefer to think the Doctor would not have been so accommodating to her psycopathic nature and nasty temperament. As a character, I found her intensely annoying; and the fact that she faces no consequences for her behaviour and betrayals really bugged me.
The other characters, we never really got to hear their stories - what made Jennver the way she was? And Jeffip? And Dela? And who really was Gyll? Maybe some more time spent on theirr backstories would have helped me to be more empathetic towards them. As it was, they largely felt just like plot devices - there, but expendable.
And The Eyeless? Really? All the words in the universe to think of to call some aliens, and The Eyeless? That's the best Mr Parkin could think of?
All in all, a bit of a mishmash - good bits, and bad bits. The Doctor, as played by David Tennant, is well portrayed here - cheeky, irreverent, serious and slightly angry and sad all in one trainer-shod Timelord. But overall, left me thinking it could have been much better than it ultimately turned out to be.