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.
YMMV: Codex Alera
Alternate Character Interpretation: Surprisingly enough, Ehren. Lord Aquitaine opines he's a master manipulator and assassin. Amara suggests that Ehren is a loyal servant of the Realm. Aquitaine notes that the two options are not mutually exclusive.
Any and all of Tavi's tactics as captain in the third book, take your pick from filling the city with sawdust and then setting it on fire when the invading army took it, dumping blood from the slaughterhouses into the river to attract sharks and the like from the sea, or having his Knights Aeris fly up and focus the air itself into a giant magnifying glass and proceeding to roast the enemies like ants.
Most of Tavi's actions in books three and four count, actually. Particularly when he finally declares himself in front of his friends and enemies and challenges Arnos (and by extension Navaris) to a duel.
When he declared his true name, the earth shook and the sky turned red. The reader knows that's because a powerful furycrafter hundreds of miles away just made a volcano erupt, but as far as the characters know it's because he's just that awesome.
Amara outmaneuvering and then leaving the scheming noblewoman Invidia and her retainers stranded, in the middle of the wilderness... sans clothing.
Bernard shooting down High Lord Kalarus from atop a moving air coach. Kalarus then proceeded to fall into the forest below at a speed probably upwards of 100 miles an hour. No wonder he doesn't show up in person after that.
Book 6: Lots of them: Starting with when Tavi successfully has several of the Vord Queen's prisoners rescued from right under her nose, and progressing to Tavi tearing down the walls of Riva, Amara killing Invidia, and the final battle with the Vord Queen.
A mortally wounded Attis Aquitaine serving Invidia her divorce papers in the middle of an intense duel.
Or how about this scene in the climax of book five. Tavi needs boats. He doesn't have any boats. So instead, he carves entire glaciers into boats, and sails them into the Shuaran harbor.
Isana is not exactly a fighter. Which makes her slaughtering 6 vord warriors at once when cornered in the sixth book that much more awesome.
Bernard taking down a vordbulk that had been shrugging off the concerted efforts of the entire Herdbane Clan with one (slightly modified) arrow.
Bernard: "Anyone could have done it."
And then High Lord Cereus tops Bernard by doing the same thing. Except instead of using an arrow, he uses himself - literally hurling himself down the maw of the vordbulk and triggering a furycrafting that destroyed its entire head, taking himself along with it, to protect his daughter and grandchildren.Manly Tears.
Senator Arnos crosses the line from "overly ambitious Smug Snake who is The Neidermeyer to his men" to "borderline Complete Monster" when he sends his troops to massacre innocent Steadholts full of civilians of both genders and their children for the sole purpose of provoking the slave rebellion into open war, all so that he can claim credit for crushing them and bolster his career. This act enrages the Canim (a ruthlessly predatory race of Blood Knights,) so much that they would prefer to reject an offered ceasefire than let him go unpunished.
Nausea Fuel: Plenty of the effects of Canim ritual sorcery. Of particular note is the fate that befalls a ritualist who tries to challenge Marok, a ritualist of the less treacherous old guard: a couple of droplets of blood and a gesture cause the offending canim to vomit up his entire digestive tract.
The Vord, especially in the second book, before we know much about them. Also the discipline collars and Lord Kalarus's Immortals.
The Canim are pretty creepy when they're introduced in Academ's Fury, though they become significantly less so as Tavi (and by extension the reader) becomes more familiar with them. The Ritualists are still fairly disturbing, though, even the decent ones- Blood Magic and all.
In First Lord's Fury, Amara serves us up this gem, noting that she seems to be in shock:
"I saw an earth fury that looked like a gargant bull knock down a building being used to shelter orphaned children. I saw a pregnant woman burned to black bones by a fire fury. I saw an old woman dragged down into a well by a water fury, her husband holding her wrists the whole way. He went with her." She paused, musing over the placid, inflectionless calm of her own voice, and added, "The second minute was worse."
HSQ: Trends steadily upward over the course of the series, until it takes up the majority of the entire final book.
Nightmare Retardant - Intentional. At the end of First Lord's Fury, Ehren reads Tavi a series of reports saying that unrest has arisen between steadholders who surrendered to the Vord and the army. The farmers keep complaining that the soldiers are killing "their" Vord— spiders and other creatures that they are using to tend their crops and livestock. Paintedin different colors so that no one confuses whose is whose.
Stoic Woobie: Araris seems to get injured a lot, and that's not even counting his motivations behind his alternate, Obfuscating Stupidity persona. But he really doesn't show his emotions to anyone but Isana, and that's after some serious empathic prodding.
Even as Fade, he can't catch a break; he tends to get picked on a lot, despite the fact that he seems to be pretty helpful around the house. Even Bernard is pretty curt with him.