I mean, I am a fan of incredibly weird books, and I will defend anything T.H. White writes to end of the Earth, but this is a freaking weird book.
It has all the great hallmarks of his more famous works, namely the same precocious, intelligent, but realistic children that are continually underestimated by adults around them. Also the brilliant, respectful treatment of animals is strong in this story, as (SPOILER) the chief villain is eventually done away with by this type of anti-hero, a scruffy rag of a lapdog named Jokey. The fun of this story is the mystery of it, as these two children get left on a supposedly abandoned rock spit in the North Atlantic, only to discover it has a bustling technological operation buried in its core, run by a mysterious gentlemen who is never known to us as anything more creative than The Master. How he came to be on this island, what he is doing there, and how he has gotten a number of people to cooperate with his bizarre plan is what drives the reader to stick with the story, even when it is completely unbelievable.
Not saying that White's other works, even similar ones like "Mistress Masham's Repose", are in anyway believable, but somehow you are more inclined to get on board with them. If you pick up "The Master" expecting it to be like Mistress Masham (as I did!) I think you will be very disappointed. It is less a tribute to The Borrowers or Gulliver's Travels and more a disturbing, slightly racist, eminently sexist, subtly violent story that ends with a tea party celebrating the narrowly averted global apocalypse. Yay?
Worth a read I'd say only if your goal is to read all of White's works--which is a worthy one! But pick up "The Once and Future King" or "Farewell Victoria" first.