I love it as a combination of factors:
- intriquing themes - it's not only an investigation of a serial killer, but it also shows the futile and desperate attempts to solve the case by someone who started too late. He rediscovers things that have been already discovered and discarded and he realises everything the day after the fair. Also, the movie shows the unhealthy obsession with serial killers just as well as the ability to completely forget a heinous crime done yesterday, because it was, well, yesterday. ”Do you know more people die in the East Bay commute every three months than that idiot ever killed? He offed a few citizens, wrote a few letters, then faded into a footnote…”
- a tribute to 70's/70's cinematography - not only it's a well-researched period piece where the atmosphere just breathes out of every shot - taking into consideration the long, wide shots with their ... "intertextuality" (sorry, my English fails me here, don't know how to put it when you have a wide shot and different "plans" within it - people very close to the camera, people in background, differing actions, important because of their context and the way they relate to one another - it was also the case with A Most Wanted Man, one of the most interesting movies camera/editing-wise I've seen in cinemas lately) - anyway, it also obviously a tribute to 70's movies and especially All the President's Men (just as Spotlight was two years earlier - even funnier with that one, because it's also about journalists uncovering a conspiracy based on true story, but actually in both cases their bosses were named Bradlee - yep, the father led the newspaper team who reported on Watergate and his son uncovered the Boston church sex abuse scandal).
- near-perfect screenplay - the investigation and discoveries are always moving forward in small, yet actually huge jumps that are almost always based on an important piece of information the character at hand says. The conversations are absolutely amazing and if I were ever to write a crime story, I'd take inspiration from here. There is a lot of small, cute touches here. ("I can't tell you anything. ... But maybe Melvin Belli could." etc.)
- the actors might not be my absolute faves in general, but they truly fit their roles. Especially Ruffalo and Downey. It's a ball to see them on screen.
- good old Fincher - there are some incredibly creepy moments (the first murder, the hitchhiker, the scene in the basement), yet they are sparse, subtle and realistic, which makes them stand out even more
- connected with the above - the movie is put together by a professional and very able filmmaker who knows what he's doing. I feel I have sat into a rollercoaster ride that takes me places and thrills me. And yeah, I've seen the movie probably 35 times or more. And I'm looking forward to seeing it again.