It's actually quite a good film if you ignore the character assassination of Zuckerberg (not that he really needs defending, just it seems a little cheap).
I don't think it's fair to call it character-assassination. He didn't paint Zuck with a pretty brush, but I'm not sure any first-tier founders made it to where they are without delivering a few cheap blows themselves. There's definitely some sense of admiration for "Zuck the Doer", not "Zuck the Dreamer".