He wrote two novels titled the Left Hand of Destiny, part 1 and 2. They were alright. While they were stereotypical in the way that Martok and Worf are about the only two honorable Klingons, it really gets weird with the villains and the means they go to. Basically the short version of the plot is some shady people from Martok's past try and overthrow him as Chancellor.
I wouldn't put it at the top of a recommended reading list, especially compared to the rest of the DS9 relaunch novels but they're alright. Hertzler does bring in a lot of plot elements for better and worse that were only briefly touched upon in the series like the Emperor, Martok's son Drax and his wife, the Negh'Var, the Hurq and other such things.