For a long time, the only book on The Wild Wild West was Susan Kesler's book which is out of print. McFarland Books and author Don Presnell do their part to fill that gap with Wandering The Wild Wild West: A Critical Analysis of the CBS Television Series.
Presnell's book lacks the first-hand production detail and photos which made Kesler's book so great, but he does offer a solid review of all the episodes and does highlight the historical context of some episodes. He also offers up some fun trivia in infographic format.
I think it's a good addition to the library of any Wild Wild West fan, and for a fan without a copy of Kesler's book, it's essential.