Many reviewers criticized the first third of Tunnels for its slow pace, but praised the remainder of the book for its fast-paced excitement, suspense, and adventure. In Britain, children's author Philip Ardagh, reviewing for The Guardian, thought the long wait for Will to discover the underground city could dull the reader's anticipation, noting that the event did not occur until page 170. He did observe, however, that when the city is reached, "fantastic fun" begins and that from then on its well-paced, exciting and – in places – frightening and bloody." He thought the characters "splendidly named and drawn". In The Sunday Times of 7 July 2007, Nicolette Jones described the book as "a good adventure yarn ... [b]ut after 460 suspenseful pages it is frustratingly inconclusive." She noted the book became a best-seller the month of its release based simply on "stories about its discovery by [publisher] Barry Cunningham, who "found" Harry Potter."
