I'm of the mind that it's the second bit. If those parts were played by Kodi Smit-Mcphee (spelling? the kid from The Road), Chloe Moretz and Haley Joel Osmont with his hair dyed red, I think the movies would've been noticeably better. I'm not knocking on the actors as they are now, but they weren't all that great when they were younger. In any case, Zodiac was a Fincher movie, so the script was probably pretty damn good.