Eisenberg does a brilliant job with the character of Zuckerberg especially. A performance that leaves the audience wanting to like the protagonist, despite every individual thing about him making him seem like an asshole. You can see that, through all the ass hole act, the backstabbing and the arrogance is just a pretty socially inept guy who needs to succeed to validate himself, a validation he'll never actually achieve.
However true to life it is, I've got to give it to Fincher, the ending is delightful. You've got the creator of the most social thing ever in human history sat alone, waiting for a friend that won't come after battling it out with the only real friend he ever had. A beautiful irony that, I hope, you only ever really get in film.