Really interesting. Contemporary western historians (mostly Roman) often wrote hagiography because they were afraid of exile. And then there's Procopius, who wrote like six complimentary books about Justinian, but also wrote a secret book about how fucked up he was which only showed up several hundred years after they died.
He spoke up for a General who had surrendered (to barbarians I think), arguing the surrender was temporary and it was to preseve their army. Emperor did not like that. Emperor said, okay, Sima Qian. You either die, or you choose castration. Sima Qian chose castration (you could pay it off, but he didn't have the money to) so he could (again, I remember it had something about his father's goals) finish the book. So he does have a pretty good grudge against the royal family, but he still analyzes them fairly.