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.
A fight between Fix and Harry has been built up since Small Favor and despite Fix having multiple advantages....Harry beats him rather easily because Harry had territorial advantages with Intellectus and a piece of iron.
Same could be said of the Redcap. Once Mab appears, no one dare continue to fight, save Maeve and Lily.
Ace goes down easily too despite earlier clever use of little folk and explosives.
Crazy Awesome: As usual, Harry's plans end up being this, but this line, where he's talking Murphy into a particular course of action, stands out as emblematic:
Harry: You have to admit, it isn't the craziest thing I've asked you to do. It isn't even the craziest thing I've asked you to do tonight.
Evil Is Sexy: The Winter Sidhe are described as "an empty void, which creates nothing but desire to fill it". They also have a tendency to wear very, very, very little.
Of note is when Maeve has been "vajazzled".
Genius Bonus: Odin is Father Christmas. A brilliant mythological joke if you've taken any comparative religion classes.
Never Live It Down: Harry having passing-on-the-mantle nookie with Mab in Changes comes up again, this time with Fix and Lily.
Nothing Is the Same Anymore: If Changes didn't hammer it in before, now there's no going back. No more Villain of the Week fun filled books, no more light-hearted adventures. The series is getting grimmer, the characters have been broken in one degree or another, and it's only getting worse. Weep for the hell these poor souls must endure.
Stoic Woobie: At the end of this, Mab certainly counts. Her daughter Maeve was possessed by Nemesis and threatened to destroy the world, ended up being killed before her eyes, and by Maeve's actions her second daughter has become the Summer Lady, keeping her from Sarissa and destroying the relationship of BFFs they had previously. The only hint we get of her deeper turmoil is when she admits to Harry who asked if she didn't like her choice to have Maeve killed, "[she] was mortal once."
The Woobie: Like Mab, but Titania is more open with her grief. She knew Aurora was evil and needed to be stopped, but Aurora was still her baby girl.