"Slow Horses," both as a book series by Mick Herron and as an Apple TV+ TV series adaptation, has received generally positive reviews for its unique take on the spy thriller genre. The book "Slow Horses" is praised for its character development, dark humor, and a plot that starts slow but builds steadily. The story focuses on a dysfunctional group of MI5 agents who have been relegated to a kind of espionage purgatory. While the writing style might seem passive at first, readers appreciate the blend of humor and intrigue, with standout characters like Jackson Lamb and River Cartwright. The book is considered enjoyable and engaging, rating about 4.25/5, with anticipation for the sequels.

The TV series "Slow Horses" is lauded for its fresh espionage approach, focusing on imperfect MI5 agents led by Jackson Lamb, played brilliantly by Gary Oldman. The show balances dark humor, complex plots, and character development, making it compelling and often suspenseful. Despite occasional criticism for predictability and some cliché elements, the series holds strong with good performances and writing. It has received Emmy nominations and is considered one of Apple's best series, with increasing popularity over seasons.

The later seasons, particularly season 4 and season 5, have been noted for adding emotional depth and humor, with season 5 being described as the funniest and most thrilling yet. The show mixes espionage with personal stories, keeping viewers engaged and eager for more.

In summary, "Slow Horses" is well-regarded as both a book and TV series for its unique take on espionage, focusing on flawed characters with humor and strong storytelling, making it a recommended watch or read for fans of the spy thriller genre.