Lol silverthorn is a leadup book much as Magician Apprentice was a leadup for the MAJOR events that unfold during Magician Master,
Its not as brilliant in scope as magician (if you view it as one book) but compared with magician apprentice the pacing is probs slightly different but as a setting for the next book i thought it was well written.
Plus it introduced a lot more back story to the Moredhel and Eledhel back story that we are still learning more about in the later series.
Overall its a good book if you are a fan of Arutha and Jimmy, the side you see to both characters is a good view of them, Arutha for once out of his calm controlled ways and Jimmy out of the city, admittedly its not quite as strong as Darkness at Sethanon or Magician but that could largley be owing to the story being quite different, no huge confrontations (aside from Baru going toe to toe with Murad)
Prince of the blood and The kings buccaneer shouldnt ever be included as part of that set of stories as they are the run up novels to the serpent war (more buccaneer than prince tho) both are worth reading although i found Borric and Erland far weaker characters than their father and uncle Arutha and Martin respectivley