Nadeko's problem, that she wishes not to be defined merely by her cuteness, kinda feels like a huge non-issue, and it doesn't really do anything to develop her character further from how it's been in Bake- and Nise-. Actually, maybe it does, but only a little: Nadeko had no character in earlier volumes, and was simply cute, but this volume, told from her perspective offers a glimpse into her self-deprecating mind, attempting to find a "self" outside of her cuteness. The thing is, this is decent enough on its own, but we've already had Nekomonogatari (Shiro) and Hanamonogatari, which both used their non-Araragi narration to do the whole "I'm not like how Araragi makes me seem" thing (with Hanekawa being imperfect in the former and Kanbaru being a bit more serious and morose than the pervert Araragi sees). If any future novels would feature a protagonist other than Araragi, we can probably safely assume the majority of the characterization therein will try to "cancel" any seen in Araragi-told novels. Hanekawa's novel was incredibly interesting. Kanbaru's... not so much, but it did well to reconfigure Kanbaru's character, having all but overwritten how we've seen her through Araragi's eyes. But this novel, I don't know. I like Nadeko more, now, but it really feels more like she's just now finally gotten some actual character traits.
Aside from that, much of the "supernatural" content of this novel is almost wasted. We get something not unlike the same thing Nisioisin pulled in the second Zaregoto book: a twist revealing much of what we've seen has been nearly all bullshit. I guess it proves the significance of the "Decoy Tale" subtitle, and overall it's pretty interesting, but, again, I don't know. Nisioisin's done this before. Never mind that the whole "you created a brand new aberration" thing was already done with the Tiger in Neko- (Shiro). "Mister Serpent" should have been the Shirahebi snake god of the shrine's name, but the concept was imbued with the delusions of Nadeko's jealous mind, granting the new aberration the drive to kill Araragi and Senjougahara, &c.
It's pretty interesting that Nadeko has been set up as the (self-proclaimed) "final boss," and the fact that the afterword mentions the next novel covering the burning of the cram school and the one after that focuses on graduation (we can assume it contains the final fight against Nadeko) shows that Nisioisin has (probably) been planning a tighter overall narrative this time around, unlike in the "First Season," which set up the events of Spring Break and Golden Week before they officially had novels, and fell into an incredibly "episodic" sequences of tales with the actual Bakemonogatari stories, somewhat insufficiently carrying characters and subplots between episodes, culminating in a true "growing into one's own" with Nisemonogatari (only to shit itself with a rather subpar offering of Nekomonogatari [Kuro]). I would hope the "Final Season" retains the forethought of this "Second Season," just with sticking to chronological order rather than shuffling things around for quasi-postmodern points.