Broken Base: Book three got some criticism from fans who found Sieh too abrasive a character to work as a narrator, and had a hard time getting through the book (which also happens to be the longest one) because of that. Others found that the story itself was so good they were able to accept this.
Everyone Is Jesus in Purgatory: Seems like a lot of people drew parallels between Oree's father in Book 2 and homosexuality. The author has stated that any connection to that effect is unintentional.
Fridge Brilliance: Things like forcing a child to make a life-or-death decision and the idea of becoming a father hurt Sieh far more than being sexually abused. And he has no problem at all having consensual sex, even if he seems to do it more rarely than most of the other gods. That's because the first two things force people to grow up, while being raped just leaves people feeling helpless. The description of "losing one's innocence" only applies in societies that think all sexual knowledge should be hidden from children. And contrary to widespread ideas created in the Victorian era, most children do have a libido, even if it only shows itself in the form of masturbation (which even embryos in utero do sometimes). Besides, Sieh's definition of "childhood" does seem to include puberty, even if he prefers the form and mental attitude of a still pre-pubescent boy most of the time.
Fridge Horror: Also, just as in the real world, quite a lot of children probably are being beaten and molested in Sieh's world. So being a victim of abuse, no matter how awful, is part of his domain as the God of Childhood, just like fatal diseases, bullying, and monsters lurking in the dark.
Jerkass Woobie: Itempas in book two. Actually one of the problems Jemisin had writing him: Portraying him sympathetically, while also making it clear that he's an asshole.
The very title of the series, which inevitably causes confusion with the far less well-regarded Inheritance Cycle.
The sex scene between Yeine and Nahadoth is very well written for the most part... and then there's the bit where she goes on about his "divine phallus." Just look at those words together and try not to giggle.
I focused on depicting the quintessential creepiness of him — the ancient soul that is always visible through his child’s eyes, the calculating adult mind which uses the wiles of a child to conceal its true complexity. But it’s hard to keep “creepy” from edging into “repulsive”. Sieh exists in a perpetual Uncanny Valley state; he looks and acts like something that he isn’t. Something we’re supposed to feel affection toward, not fear.