Molly Young at the NYT:
Agatha Christie’s best books have crisp dialogue and high-velocity plots. The bad ones have a Mad Libs quality: feeble prose studded with blank spots into which you can picture the prolific Christie plugging a random “BODY PART” or “WEAPON.” In a 1971 study of English crime fiction, Colin Watson snickered that Christie “seems to have been well aware that intelligence and readership-potential are quite unrelated.”
Watson’s barb was unfair. Few readers turn to detective novels for complex cerebral rewards. Detective novels are games, and require a different method of evaluation (and construction) than works of capital-L Literature. Christie understood this.