This slender novel is a thought-provoking, relatively quick, and relatively enjoyable read. Regarding the central character, the real-life poet John Clare, I come from a position of ignorance and it is quite possible that had I known more of him I would have found more to enjoy, or at least more to recognise. But the book is explicitly not intended as history and I think as a portrait of insanity it is effective without any prior knowledge.
The prose is at times quite luminous, and in describing the natural world Foulds has a genuine talent. Certainly he has made great effort to be poetical in his descriptions, and evidently this to widespread acclaim. However I am hesitant to add the possible heresy that at times he seems to have tried rather too hard to find the "right" adjective (often, that is, a strikingly incongruous one). I don't say this in exasperation, since in fact Foulds' vocabulary is not especially showy (though there is a whiff of ostentation), but its usage can greatly affect the flow of the narrative -- it takes a fine judgment to know when to employ some arresting terminology and when to let the sweep of the story carry the reader along. Foulds achieves beauty in the minutiae and in the countless vignettes (the scene in which a deer is eviscerated and cooked is majestic), but this does not to my mind translate into a beautiful novel. In this regard I was reminded of a previous Booker winner, John Banville's "The Sea", which I felt sure to enjoy after the opening pages, but whose pretensions ultimately dwarfed its achievements. That is an unfair judgment in this case (and maybe in the other!) -- there is little of Banville's desperately overwrought prose here, and Maze is probably a superior work to Sea -- but veterans of Banville may have an inkling of what to expect.
My other more serious gripe is with the highly fractured plotting and its consequences. The book's several "chapters" of consecutive seasons are each broken into numerous bite-size chunks whose length can be as short as a few lines, and which are rarely longer than three or four pages. Although this is a great benefit for anyone forced to read in brief interrupted sessions (e.g. on the tube), this skipping around is problematic for delineating and developing characters, and since the whole piece is barely 200 pages, it results in a sizeable cast of largely functional caricatures. There is a stock villain who rapes the patients, a lunatic who worries about God and the National Debt and nothing else, the "Jane Austen" daughter who fantasises about love and marriage to the exclusion of all other interests, and so on. Even the real-life characters are a little thin -- Dr Allen at the asylum, for example, is a central figure but has been rendered narcissistic to the point of farce, and without the shred of a redeeming feature he is not just unpleasant (none of the characters are especially likeable), but also rather implausible. Only Clare, who enjoys the bulk of the most virtuosic prose, comes alive as an individual, and the portrait of his descent into madness is poignant, compelling and thoroughly credible.