I felt that the storytelling in
Zodiac was quite smooth throughout, not just in its second half (which pretty much took place exclusively from Graysmith's point of view alone), but in the first one as well, as, even with its ever-shifting perspectives, the film remained constantly propulsive and engaging from the way it used every single character and scene to advance a new fact or development, steadily building up the case one brick at a time as Fincher knew that, as a serial killer procedural, the case is the true star of the film, which is an approach that is consistently utilized throughout the film, and makes perfect sense to me.
At any rate, it doesn’t make sense to me to criticize
Zodiac for a lack of social relevance, as, even with its steady stream of details, it still fit a lot amount of commentary into its running time regardless, with its portrayal of the susceptibility of the public to irrational panic in the way that the entire Bay Area goes crazy in the light of the killer's threats, the dilemma the publishers of the Chronicle face when they have to decide whether printing his letters in the newspaper will temporarily placate him, or simply feed his hunger for public attention and fear, and encourage him to kill and terrorize even more, as well as with its critique of the mass media's role in adding to said public panic (one that's done partially in the pursuit of just getting more eyeballs glued to their papers/reports), which is a point that is not just implied, but basically expressed straight-up by Avery himself: "Do you know more people die in the East Bay commute every three months than that idiot ever killed?".
As for the point about the characterizations, Graysmith's wife can indeed be considered a stock, ignored wife, but I was still impressed by the way that, in-between all the minutia of the overall investigation, Fincher still managed to find a way to neatly fit in the defining beats of that sub-plot (from their first, uber-awkward date, to the final wedge that Graysmith's obsession drives between them) into the film, but I can't think of many other examples of obsessed, amateur detectives in films, so I don't see how Graysmith is a clichéd character on his own, and as for the main suspect, him being a blue collar creep is simply an accurate reflection of the real Arthur Allen (as most actual serial killers tend to work menial (at best) jobs anyway), so calling him a clichéd character is like when that guy on RT complained that the movie had a "shaggy dog ending" because the killer was never conclusively identified; it's like, but that's how it happened in real life (the movie itself even pointed that out by contrasting the lack of closure with the "Hollywood ending" of
Dirty Harry), so... that's kind of the whole point?