If you don't have plans to see this movie, you can check the spoilers here and then come back.
I did not like the first 15 minutes or so of The Social Network. The very first scene drops you too quickly into fast-paced Aaron Sorkin dialogue without introducing you to the principals and then the subsequent sequence of tech-heavy action again doesn't give you a way in. However, get past that rough start and this is an excellent movie bearing the very best marks of screenwriter Sorkin as well as director David Fincher and their trademark specialties on a compelling story packed with fantastic acting performances. The tale of Facebook founder Mark Zuckerberg and the friends and enemies he wittingly or unwittingly lied to and/or betrayed on his way to the top made for a book I could not put down in "The Accidental Billionaires," and the creators of this film did yeoman's work taking that framework--which was certainly not quite ready for Hollywood--and translating it to the cinematic medium.
Without question in my mind the shining star of the entire piece is Jesse Eisenberg, who as Zuckerberg leaves his previous roles as hapless nice guys way behind and creates an unnerving yet memorably and believable character (as reportedly the portrayals here were based not on the real people but on Sorkin's dramatized script) like few I've ever seen. Eisenberg's Zuckerberg is like a robot or reptile who chillingly and without interruption moves from one task to the next with single-minded purpose; when he displays human emotions for even a moment, it's as if he's simply straining to mimic those around him rather than feeling for himself, and it works perfectly. Eisenberg captivates you with what a frankly terrifying genius and honestly borderline (albeit relatively harmless) sociopath his Zuckerberg may be, while also carefully making you feel flashes of sympathy, but only flashes; when he feels remorse, it looks more like a glitch in the system than a human emotion.
As Napster founder Sean Parker who leeches onto Zuckerberg's burgeoning empire, Justin Timberlake comes in with the perfect combination of smooth charisma and childish paranoia; the people I saw this movie with felt like he wasn't straining much, basically just playing "Justin Timberlake but as a bit more of a douchebag," but I'd disagree, as he displayed true vulnerability in some scenes that made the character for more complex. Andrew Garfield is the guy we're supposed to emphasize with, Zuckerberg's hapless buddy Eduardo, and he does fine, but I wish he'd been given more to work with. As the alpha male Winklevoss twins, from whom Zuckerberg "steals" the Facebook concept, Armie Hammer--aided by body double Josh Pence and some impressive CGI--displays both power and poise, plus he gets off some of the best lines of the movie.
I'm impressed how well Fincher and Sorkin paced the movie, as it comes in at a smooth two hours and never leaves you bored (it could have been longer). They definitely improved on the book in many ways, using it as a guide but not becoming slavish to it. Honestly part of me wishes I hadn't read the book first if only because I knew that two of the film's primary motivations for Zuckerberg (losing a girlfriend and jealousy over Eduardo's place in the Harvard Final Club hierarchy) were either trumped up or manufactured, but while the actual "he more or less did it because he could" reasoning is fascinating, it probably wouldn't make for a great film.
Oh, and before I forget, Trent Reznor's soundtrack seriously added a lot to the movie.
This was a great story that was going to be either an easy hit for smart filmmakers or fumbled badly by guys looking to make their own mark, and I'm glad it wasn't the latter. I'll need some time to let it settle before I decide if it's the primo Oscar bait a lot of people are proclaiming it, but I certainly liked The Social Network.