Alas, Poor Scrappy: Atticus privately mourns Fjalar, whom Brighid incinerated. It's very hard for readers to feel sorry about it though, given what he attempted.
Alternate Character Interpretation: Hearne takes quite a few liberties in his interpretations of several mythological characters including the Celtic gods Aengus Óg and Brighid. The worst is Thor who goes from one of the most heroic gods in all of mythology and protector of mankind to a sadistic sociopath.
Thor's case, at least, is justified by explaining that Odin ensured that his stories and the others of the Norse were written down, at least in part to make them look good.
Author's Saving Throw: The scene in A Prelude to War where Granuaile beats up Loki. It was probably meant to make her more likable but it comes so out of nowhere it's hard to take serious, and is later amended somewhat with the notation that Granuaile got insanely lucky and she knows it.
Critical Research Failure: Susannoo and Shango are among the gods named as having been tricked by Thor into not having their stories written down and largely forgotten by the modern world. But Susanno's stories were written down centuries before the Prose Edda was compiled and he has served as a major figure of Japanese religion, art, and culture from ancient times to modern day. The same for Shango in regard to west African cultures and modern religions like Santaria.
In the very next book, Shango appears and is described as "quite beloved by [his] people", so this was likely an instance of Unreliable Narrator on Perun's part, who said the above.
Darkness-Induced Audience Apathy: There have been a few complaints to this effect, even In-Universe from Granuaile. Atticus, while firmly on the side of good, is more than willing to let a few crimes fall by the wayside in the service of what he views as more significant goals and many many of the gods operate on Jerkass Gods, and get away with it mainly by virtue of being gods.
Aenghus Og drawing on so much power to open a portal to Hell that it kills the surrounding Earth for like twenty square miles. As a Tuatha de Dannan, Aenghus Og is a druid whose tattoos connect him intimately to the planet. Atticus does not take it well.
Hel showing up in the body of the recently deceased widow Mac Donagh. Another case of It's Personal for Atticus.
Narm: Ever since she started getting p.o.v. chapters, Granuaille can hardly pass one without obsessing over her step-father even when she's got more important things to be worrying about, like the impending end of the world or death by divine snake venom.
To some, it stops once she finally gets around to dealing with him.
Rescued from the Scrappy Heap: Granuaile in A Prelude to War by beating up Loki so bad he loses some teeth. This lasts about two of her chapters before she jumps right back on top by using her powers for what is explicitly petty revenge on her step-father for being a jerk while acting like she's in the right the entire time.
Staked begins a more coherent process of rescuing her from the scrappy heap by finally getting around to that petty revenge on her step-father and realising a) that it is pretty petty, b) that it left her feeling part great and part terrible, c) and, nasty as he was, she just beat up an old man (hence the feeling terrible part). As a result, she not unreasonably worries if the appellation of 'Fierce Druid' that the elementals give her is more than just a badass nickname, and is instead a warning about her Hair-Trigger Temper and where that could lead. Her POV sections also make clear a definite realisation that she got lucky with Loki, as if she'd not caught him in what was close to a perfect situation for her, she'd have been crushed.
The Scrappy: Granuaile, somewhat, from Hunted onwards, not coincidentally coinciding with her introduction as a p.o.v. character. Among other things, she is incredibly vain, plays Tsundere right after the love of her life returned from the dead and acts as though most other people don't deserve her company. She gets better. Arguably.
Take That, Scrappy!: In Staked, Laksha finds herself in the body of a woman who is abused by her entire family. Granuaile tries to convince her to leave and finds herself harshly rebuked by Laksha, who views her circumstances as karma for a lifetime of evil, and who points out that Granuaile is a wealthy globe-trotting Druid who can pull up stakes at any point and be completely fine, which other women in similar situations as Laksha can not claim. Laksha says that she is on her own spiritual journey for redemption whereas Granuaile if anything has gotten worse since they first met. Doesn't do anything to change Granuaile's mind though - though she does apologise once Laksha rebukes her and she realises that Laksha's host was suicidal and Laksha is trying to persuade her to take back her body some day, and she does kind of have a point when she says that Laksha can go any time she likes.
What an Idiot: Atticus gets neck deep in trouble thanks to his Honor Before Reason insistence on helping Leif and Gunnar, in defiance of more than two millennia of running away from fights he doesn't know for sure he can win and the warnings of the Morrigan and Jesus (who is omniscient, or at least close enough for it not to matter) that it would be a monumentally bad idea. He goes through with it anyway, and things go tits up fairly quickly. He's managed to piss off two and a half pantheons (The Norse and the Romans, with the Greeks getting involved only out of solidarity with the Romans), with another (the Tuatha de Dannan) using him as a betting chip for their own ends. A whole slew of thunder gods from just about every pantheon on Earth would have his guts for garters given the slightest inclination (they tend to take exception to lowly mortals killing gods, even if no one likes the Norse). By the time he actually wises up and ditches Leif, Leif runs off and tattles to the vampire nation, who have allied with the Norse Dark Elves to finish off the last remaining Druids due to an unconnected grudge. And things are just getting started.
The Woobie: Surprisingly enough, The Morrigan. She hated being a Jerkass God, but all of her attempts to change herself were met with abject failure, so she ultimately let herself be killed.