I was so happy to see these characters in action again that I cheerily overlooked a few niggling problems in the first Nisemonogatari. The second volume beats you in the face with them till you simply can't ignore them, and start making mental lists of all Nisioisin's greatest failings as a writer, virtually all of which are on display here. The only thing he doesn't do is explain the deductive process exhaustively.
His absolute refusal to allow any of the characters to interact with each other is the main beef I have with him right now -- even Karen and Tsukihi, largely created for these two volumes. While great characters, they are both little more than foils for Araragi himself. Either he forgot to figure out how to make them interact with the rest of the cast, or he is blissfully unaware of how much we'd like to see that shit happen. I mean, seriously, the entire first half of this book revolves around a dangling carrot -- Araragi is going to introduce Karen to Suruga. A hundred and fifty pages build up to this...and it is over in less than a page. Araragi just fucks off to talk to Hachikuji, and leaves the two of them to get on with it offscreen. I was so god damn angry I stopped reading for two days.
He seems pathologically reluctant to actually show us shit. If Senjogahara has had a major personality change since we last saw her, how hard would it have been to actually show us this? Possibly with the extra carrot he dangles on the last page, where Araragi finally mentions her to one of his sisters? Instead, there's a hideously placed extended wall of exposition that begins by redundantly explaining her old personality in case someone started with this book, and then equally laboriously explaining the change before telling us she's not going to appear this time around! It goes well beyond boring to actively fucking insulting!
As much fun as Shinobu goes to Mister Doughnuts and some of the other random bits scattered throughout the volume are, they don't really make up for the number of obvious plot ideas we'd much rather be reading about.
Add into that an uncomfortably eroticized scene where he brushes his sister's teeth, a scene far too disturbing to feel at home in a frothy thing like this, and something he's already done successfully in a different series, and a climax that depends on the villain's position being morally superior to Araragi's, when viewed objectively and that utterly fails since no one in their right fucking mind would have the slightest sympathy for the reprehensible fucks, and we pretty much have the full compliment of failings.