These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Complete Monster: Bekter, anyone? He raped a prepubescent girl, stole game that Temujin worked hard for and was willing to let his family starve as long as he had enough for himself.
Guyuk and Arik-Boke, in Conqueror, also contend for the title. However, due to Deliberate Values Dissonance, lots of main characters (like Hulegu) would be this to a modern reader, even Genghis.
There's also Eeluk, who betrays Yesugei's family after he dies, at his funeral, steals the heirloom sword, and tortures Temujin when he's captured.
Squick: Conn Iggulden has a disturbing tendency to expound in great detail about characters excretory functions, particularly at the moment of death. It's nicely averting one trope, but seems excessive a lot of the time.