WHAT I LIKED: David Fincher's 'Zodiac,' isn't really a serial killer movie at all (in fact, there's no serial killer in it) - it's more of a journalistic thriller come character study. It focuses on the people trying to catch the real-life "Zodiac," over a number of decades, and whilst it's largely all about the case, it also becomes about how the case affects and consumes the investigators' lives. With regards to the journalistic elements which take up the majority of the runtime though, what makes things work most of all is just that the plot is so inherently engaging because you want the guy to be caught. That's emphasised tenfold by the fact that Fincher directs the few murder scenes absolutely brutally so your hatred for the Zodiac is increased further, and also because you care about the people trying to catch him so much.
In fact it's that character-building stuff itself where the most interesting stuff arguably lies, especially as the performances from Mark Ruffalo - and Jake Gyllenhal in particular - are so great. As the film develops, an increasingly greater amount of time is spent at home with them on rainy nights to see how the cold, hard reality of desperately and obsessively pursuing something like this eats away at the normalities of home life a-la-Michael-Mann. As characters drop off from the case and only Gyllenhaal's is left standing, the desperation around completing the task not only overwhelmes the film's obsessions with its intricacies, but also makes for a pretty melancholic experience which is especially engaging as things start to (and indeed fail to) draw to their true close.
WHAT I DIDN'T LIKE: Particularly in the first half, much of the script is simply made up of characters meticulously stating new evidence to further the plot, and whilst that means it avoids any potential for grandstanding, it makes scenes very wordy and almost perfunctory. That wouldn't have been such a problem had everything been given the urgency of something like 'All the President's Men,' from the get-go, but until Jake Gyllenhaal's character really starts to get his teeth into the case, any hunger in the investigators largely begins with benevolence - a feeling of indifference and levity which is emphasised to the audience by the occasional stylistic choice and the often bumbling soundtrack.
VERDICT: Whilst 'Zodiac's plot is inherently compelling, the script's delivery is often very mechanical. The interesting stuff really lies with the obsession and resulting melancholy of the characters, and luckily that takes centre stage as the film develops.