I have to agree the book left me rather disappointed too. The plot was too wordy, there was way too much politics which added little to the outcome of the story and there was far too little interaction between Avon and Servalan.
The chemistry between these two characters was what made seasons 3 and 4 of the TV series watchable, but this chemistry was totally ignored in this book and to have barely two pages of dialogue between them was an awful waste.
I personally would have finished the story with Avon admitting that Orac had been destroyed in an accident, and mindful of the fact that she lost her power within the new Federation and of her advanced age, Servalan decides to join forces with Avon, and let their adventures continue in future stories. Overall I'd give it 6.5 out of 10