Having read the novel, I couldn't watch the movie unspoiled, so I can't tell you how it comes across to the unwary. The trailer, as opposed to many a trailer, has been very careful not to give away the big twists, so I expect the producers are counting on the fact a part of the audience has no idea. It's the type of story that provides a different type of reading/viewing pleasure the first and the second time around, and thus, I'll be careful with the spoilers, too, separating the review into unspoilery and spoilery comments.
First of all: it strikes me that if The Social Network felt like more imprinted by Aaron Sorkin, who wrote the script, than by Fincher as the director, this is even more true of Gone Girl, where the script is an adaption by Gillian Flynn of her novel by the same name. Or maybe I should say: David Fincher in both cases serves his writers well and adapts to them? (As opposed to the conventional view where the director's vision reshapes everything.) In this particular case, there is a gleeful malice to the dissection of both romance and suspense story tropes which I recognize from the novel and which came across to me as feminine. It's also interesting to compare this to Robert Altman movies because Altman is a director who specializes in presenting unlikeable characters which (not always, but often) nonetheless have interesting, often satiric stories, but his type of narrative comes across as masculine to me. (For that matter, the Sorkin/Fincher Social Network did, too, which also offered unlikeable characters - no, I didn't like Eduardo, either - in a fast paced narrative.) Gone Girl, by contrast, I couldn't see as an Altman movie. It would have weighted its narrative emphasis and view points differently, for starters. (And there'd have been lots of overlapping dialogue. :) )
Acting wise, Rosamund Pike does most of the heavy lifting; she has the trickier character to play, and she does it beautifully. (Also with great comic timing, which is more important than you'd think.) More in the spoilery section. Ben Affleck's role is actually pretty straightforward by comparison; it's what the audience (both on an in-story and a viewer level) projects into him that counts, and you can see why Fincher cast Affleck, who from his image could plausibly be either creepy wife killer or wrongful suspect and at any rate can do that aura of seediness of someone whose best days are gone and whose charm, if employed, has become somewhat smug routine. (For a poignant version of this, see Hollywoodland, where he plays murder victim and ex TV Superman George Reeves in the flashbacks. But George Reeves is tragic, and Nick, his character in Gone Girl, is anything but.) Everyone in the supporting roles has great fun, especially Tyler Perry as Nick's slick lawyer (a true comrade of Breaking Bad's Saul Goodman) and Kim Dickens as shrewd Detective Rhonda Boney, who investigates Amy's disappearance and possible murder. (While the novel is strictly divided between Nick and Amy as first person narrators, the movie leaves their povs briefly now and then to show us Rhonda and her sidekick investigating and exchanging views.) I also really liked Carrie Coon as Nick's twin sister (Mar)Go. Now I have a soft spot for sibling relationships anyway, but in the novel I couldn't quite believe in Go and Nick as twins who grew up together. Without a change in dialogue or narration, the movie sells me on them via the acting; Coon and Affleck have that kind of easy rapport complete with occasional exasparated/disgusted eyeroll on Go's part. David Clennon and Lisa Banes as Amy's parents have only a few scenes, but they're absolutely golden; Lisa Banes especially, in the scene where she ends her plea for people with information about Amy to contact them by naming the newly established website for this; the slight pause before she says "dot com" makes it a maliciously comic masterpiece.
Speaking of Amy's parents, succcessful children's authors famous for their book series Amazing Amy, while both novel and film obviously target the media and the way it builds up (and destroys) public hate and sympathy figures, it only occured to me during watching that Amy's parents and Amy's backstory also makes it into an entry in the " parents/guardians/adults-with-close-relationship-to-you who write children's books and use fictionalized versions of you in them really suck" chronicles (for fictional versions, see A.S. Byatt's The Children's Book; in real life, step forward, James Barrie and Lewis Carrol). By necessity, the film had to leave out some things and could, for examply, only briefly sketch and hint at at Nick's background with his parents, but Amy's background with her parents is really important to who Amy is, and the film manages to convey it all in a flashback scene to the latest Amazing Amy book launch which Amy takes Nick to early in their relationship. (The art department also had fun with the Amazing Amy book covers.)
Now, on to some observations about both film and book which spoil the various twists and ending, hidden beneath spoiler white: In absolutely every review of the book I've seen, it's mentioned that it has not one but two unreliable narrators. Welll, yes and no. Or rather: only until half of the novel. Nick's an unreliable narrator during the first half in as much as he omits some information and later casually drops bombshells like the one about having an affair with his student from the writing class in a "oh yeah, did I forget to mention this?" manner, which serves to make a first time reader suspicious what else he's not mentioning/leaving out; also, his memories of Amy as manipulative conflict with the image Amy creates of herself in the sections of her diary (covering the years from her meeting Nick till her disappearance) that serve as counterparts to Nick's present day narration, and in which he comes across as a budding textbook future wife killer. However, around half point of the novel we reach the first big twist: Amy's diary is a fake, fabricated by Amy along with a lot of other Nick-incriminating evidence in careful preparation of her disappearance in order to frame him for her murder. Nick, while an adulterous jerk, is not an abuser or murderer. From this point onwards, both Nick and Amy continue to narrate the novel in the present, with the suspense question going from "did Nick murder Amy?" to "will Nick manage to get Amy to come back in order to save himself?" and "will Amy get away with it?" After this twist, there is no indication either Nick or Amy are unreliable narrators, or that what they describe happening in the present isn't exactly what happens. Now, one of the things I was most curious about was how the film would manage Amy's diary entries. Because it's one thing for a book to declare that part of what you've just been reading was actually not true because it was written by one of the characters with an in-story purpose to mislead other characters, and another for a visual medium to declare that those scenes you just saw didn't really happen this way. The film pulls this off two fold; one, every Amy flashback in the first half is framed by a brief glimpse at Amy's hand writing the relevant diary entry, so that the audience is reminded what they see is straight from this diary, not from an "objective" pov; and two, Amy's voice over in the second part as well as a scene between Nick and Rhonda makes clear which parts of the Amy flashbacks really happened (all until they're both unemployed; the gameboy scene, the argument about having a child and Nick pushing Amy were faked), and which didn't. Most of all, though, it's Rosamund Pike's performance which holds it together. In the novel, the transition from vulnerable victim!Amy in the diary to gleeful sociopath!Amy in the present day is jarring - and meant to be, since the former was a creation of the later. In the movie, you can see Amy's capacity for faking a facade while being seethingly angry - at her parents - in the book launch scene, as well as her joy in games, verbal and mind games, in her early relationship with Nick. Conversely, in the second half when Amy is vengefully watching Nick being torn apart by the media on tv with a new aquaintance, she within a lie tells a true story of how she found out he was cheating on her, and here she comes across as genuinely hurt, sociopath or no sociopath. And as I said: being the child of novelists who kept rewriting her life into a more perfect version through her childhood works as a suggestion as to one (not the only) reason why Amy became the way she is. Mind you: the film ditched one of Amy's victims from the book, the girl from her school whom she framed as a Single White Female type. Which in the movie leaves us with the ex boyfriends and Nick, none of whom are inviting much sympathy - though Nick, by virtue of his sibling relationship with Go and by being a considerate cat owner even when framed for murder , invites just enough that one doesn't want to see him dead for something he didn't do -, so the main feeling when watching Amy framing them is amusement at her ruthless cleverness. (I was wondering whether casting Neil Patrick Harris as Desi would make us feel sorry for the guy, but no; he comes across as the proverbial Nice Guy and so creepily obsessed with Amy that one could almost hear Chicago's "He had it coming" when the film got to its sole actual murder.)
Another thing, to explain further what I meant about male and female narratives: one obvious movie to compare this to is Hitchcock's Vertigo, because Vertigo, too, has a mid-story twist/reveal showing that the male main character has actually been set up and that the person whom the audience had been watching for half the film never existed but was an artificial creation. But the next emotional twist in Vertigo is to feel sorry for Judy as she's forced to recreate the "dead" Madeline for Scottie, with the scene in which he makes her completely transform being one of the most emotionally violent on film without any physical violence whatsoever. Part of what makes this scene so memorable, so intensely uncomfortable and great is that while on one level you know what Scottie does to Judy is horrible, on the other you can understand why because the movie sold "Madeline" so well before to the audience, too. (And then there's the meta level of Hitchcock creating a Hitchcock blonde by tormenting an actress, obviously.) Judy is an instrument - first for the real Madeline's husband, then for Scottie -, not a player, and she dies for real at the end; despite the mid story reveal the audience remains in Scottie's pov.
Meanwhile, Amy is no one's instrument, she's the mastermind. Not an invulnerable one or infallible one; she underestimates, very much for snobbish reasons, the dangers of the couple next door in her hideout, plus Nick once he's figured out what exactly is going on successfully manages to manipulate her back to save his life. But she is the stringpuller, and the ultimate winner of the tale. After the mid story reveal of Amy's survival and true nature, the narrative doesn't invite you to feel sorry for her but to share in her glee as she makes her unfaithful husband squirm. In Vertigo, Judy's post-reveal submission (and Scottie going from sympathetic hero to oppressive obsessive) is the emotional twist. In Gone Girl, Nick does the submitting. And how.
Now advance publicity for this movie made a big deal about a changed ending. This must have been so the people who already read the book would go and see the movie anyway, because the ending is exactly the same, the meanest twist on a "happily ever after" since Altmann's The Player. And honestly, I can't imagine another one for this particular story. Amy being exposed and arrested, or Nick snapping and actually killing Amy would both feel like a let down by comparison. To misquote Jesse Pinkman from Breaking Bad, it's not that Amy and Nick deserve each other, but Amy and Nick deserve each other. Poor Go, though. And poor future spawn.
In conclusion: for this spoiled-by-the-novel viewer, the movie was a witty, biting and smoothly proceeding entertainment. Very watchable.