Where you might, unsuspecting of Fincher's genius, reasonably have expected a thriller in the vein of 'Seven', you are confronted with something wholly different.
Although 'Zodiac' deals with Hollywood's umpteenth serial killer ("based on a true story" to boot) its focus lies not on any gruesome killings or heroic police detectives, but on the ups and downs of police investigation.
It has a realistic ring to it, insofar that years pass, people come and go, suspects and theories are considered then discarded, then sometimes reconsidered - and in the end (spoiler alert) the killer goes free, thus embodying the ultimate failure of the legal system.
This ought of course to make for a tedious film, especially for someone like yours truly who has all but given up on detectives and serial killers on screen.
It is, accordingly, a measure of Fincher's talent (So I may be over-insistent about it. Sue me.) that I not only sat it through to the end, but couldn't even focus on my magazine-browsing which I normally have no trouble carrying out while watching TV.
So all of the above AND Jake Gyllenhaal, too! How lucky can a girl get?!