Originally I was going to write this review under the assumption that everybody knew the basic details of San Francisco's legendary Zodiac Killer: how many murders he's connected with, how long his killing spree lasted, and whether he was ever identified or caught. But my wife informed me, after we saw Zodiac, that she knew none of this going into the movie. So if you don't know anything about the case, perhaps you should stop reading now. Although it may serve you well to read it, so that you won't be as disappointed with this film as I was.

Here's the thing: for those of us who have even a passing knowledge of the case, we know that, like Jack the Ripper, Zodiac was never caught. We also know that he mysteriously stopped killing after the five murders that were connected to him. And since Zodiac is based on Robert Graysmith's exhaustive true crime tome, we can guess that the movie doesn't bump off Graysmith himself (played by the ever-earnest Jake Gyllenhaal). Thus the handful of suspenseful scenes where Graysmith's life is "in peril" are actually un-suspenseful, because we know he survives.

Since they can't make us fear for the man's life, Fincher and screenwriter James Vanderbilt walk a fine line between critiquing Graysmith's pathetic, almost pointless obsessiveness, and celebrating the fruits of that obsessiveness: after all, Graysmith's book became a bestseller and a Hollywood film. They want to make a character study, a police procedural, and a whodunnit all in one. Which I'd support – if only it worked.

The main problem is not just that we already know that we'll never see Zodiac brought to justice, and that we already know that none of the main characters are going to get whacked ( Zodiac "officially" ended his killing spree in 1969), but that Graysmith's devotion to solving the case – and mind you, he was just a newspaper cartoonist who only got involved out of curiosity – continued for almost twenty years. This means that, two hours into this overlong movie, Jake Gyllenhaal is still going nuts over every shred of evidence, long after we've gotten over the disturbing early murder scenes.

In short, I lost interest way before Graysmith did, so I couldn't buy into his obsession. Zodiac would have been a much better film if we could have been made to identify with this character, or at least see the value of pursuing this years-old, increasingly uninteresting case.

I lay part of the blame on poor Gyllenhaal; again, "earnest" is the best way to describe the actor and his work. He tries so hard! Yet there's a blandness in his portrayal of Graysmith. Decades go by, but he doesn't show the scars of his obsessiveness or even the passing of time. (It doesn't help that the actor's trés-2007 haircut remains exactly the same, whether we're in 1969 or in 1983. If the actor had let himself go "full '70s" like costars Robert Downey Jr. and Mark Ruffalo – both of whom turn in effortlessly fine performances – then it wouldn't have been as distracting.)

In 1971, while the real Zodiac was still on everybody's minds, the cop thriller Dirty Harry came out. It's no secret that the Clint Eastwood classic was inspired by the killings. (Fincher's Zodiac even includes a scene at a San Francisco screening of the film.) Fictionalized as it is, it actually tells a more gripping, more engaging, and more satisfying story about Zodiac. If you haven't seen Dirty Harry yet, give Zodiac a miss and catch that outstanding film instead.