'Gertrude and Claudius' is the only Updike novel I've ever read, so I came to it with no preconceptions about his work. However, I am a long-term 'Hamlet' fan, and so I was intrigued to see what he had done by refocusing the story upon the doomed Queen and her second husband.
It is delightful! I was amused by the shifts reflected by the name-changes and the subtle costume changes that reflect the different versions of the story (Saxo Grammaticus, Belleforest, & c.). Part One is 11-12C, but by the end of Part Three, where the novel finally catches up with the play, we are approaching the Renaissance. The falconry symbolism is particularly lovely.
The main characters are engaging: Gerutha/Gertrude is a likeable, warm-hearted woman. She is Queen by birth, but because of her sex, real power eludes her: it is always wielded by men. Horvendil/Old Hamlet is an unimaginative, rather crude Viking war-lord: a tough killer, a rapist, yet there is poignancy in his remark about wanting to show his bride his "morning self", in explanation of his drunken sleep on their wedding night. Feng/Claudius is a cosmopolitan, imaginative adventurer who has fought his way across Europe to Byzantium, and quotes the songs of Bertran de Born. (I was reminded of Rognvald Kali, the Jarl of Orkney who wrote trobador songs for Ermengarda of Narbonne.) Corambis/Polonius and his sensitive daughter Ophelia are also well-drawn. Amleth/Hamlet himself is mostly off-stage, but even as a child, he shows signs of selfishness and spite. (Updike rightly points out, in a quotation from a critic in the Afterword, how destructive the prince's quest for vengeance is: for one man's death, many others, including innocents, will die.)
What also appeals (especially to the older reader) is that the novel gives us a passionate, tragic love story about experienced middle-aged people - a plump 48-year-old matron and a grizzled warrior in his late 50s - *not* glamorous young romance-novel stereotypes. The apparently 'happy ending' of the novel is heartbreaking. By the end, the reader, who knows what Shakespeare has in store for the characters, is actively willing the play to end differently, willing them to "get away with it". Updike has not just expanded the protagonists' lives; he has enabled us to *love* them. It seems to me that not many modern novelists have that gift.