While this is arguably one of David Fincher's best movies, it's not quite what you would expect.
When any movie is made about a crime that has captured an entire nation's attention for decades, it usually does a lot of finger pointing, it's over sensationalized, and doesn't really have anything remotely close to true facts.
This is basically Fincher's thesis on who the Zodiac could have been. If you're not really into cop dramas and more into gruesome killings and action, this probably isn't the movie for you. Most of the killings take place early in the movie, with the rest of the time being spent on the cops and cartoonist who become obsessed with figuring out the still unknown killer's identity.
Some horror fans may find themselves bored with this over two hour long movie if they go into it expecting the usual slash and dash serial killer fare. But if you like Fincher and true crime, this is a movie for you.