In short: just a handful of misquotations and easily verifiable lies.
I want to give this the best and most impartial review I can, so here goes my disclaimer: I've been following Wikileaks work since circa 2009 and I admire it a lot. I never got much information on the organization's personnel though, just the regular news on Assange, and also some news on Bradley Manning (not a member of WL, but a self-confessed source for the Iraq/Afghanistan war logs). Having watched some of Alex Gibney's previous documentaries (Enron, Taxi to the Dark Side, Park Avenue - all quite good, although a little biased to the left, esp. the last one), I was looking forward to watching this one, since I also knew beforehand it'd focus on Assange and Manning, not so much on the organization itself, so that maybe I could finally shed some light on their personas.
Unfortunately, it was just a waste of time, I got out of it with basically the same information I came in with. That's because, specially from the middle to the end, there are so many factual mistakes that you learn nothing; there's no new data, just smear. And this is easily verifiable, in fact so easy that Wikileaks published the full transcript of the film (just google "transcript we steal wikileaks"), with annotations on the side pointing to where one can find the original material (eg. the link to the guardian or nytimes site) that bases what is being said by the narrator or interviewee, and showing how the source material irrefutably contradicts what is said upon it.
There are also cases where crucial information is lacking. For example, Assange's "rape" affair. The justice4assange website covers the issue thoroughly, mentioning that there was no trace of Assange's DNA in the condom he allegedly teared, that the Swedish authorities only want to extradite Assange for questioning (no criminal charges were filed against him) but do not allow him to be questioned at the Scotland Yard by a Swedish authority nor accept that his questioning is undertaken via internet in real-time (Skype), that Assange accepts to fly to Sweden if the Swedish authorities guarantee that he won't be extradited to the USA once in Swedish soil (such guarantee was denied), etc. None of this is mentioned in the movie, though it is at hand for anyone that searches 5 mins for it.
There are so many dirty tricks in the edition of the movie that makes it impossible to think that Gibney didn't make the misquotes on purpose. I don't know what his reason was, but he surely knew too about most, if not all, the factual mistakes highlighted in WL's transcript. Anyone that researched WL or Manning for some days would end up knowing it.
My humble opinion: this film is just a 2 hours long ad hominem fallacy on Assange and Manning, trying to portrait them as "troublemakers" coming from difficult childhoods/backgrounds so to shift the focus out of the politics that created the leaks and into these "troubled souls", reckless children that act out of hybris and not moral principles. I think even this could be worth watching if it had any factual support, but it surprisingly manages to ground itself only on lies. As it is, it's only interesting to watch if you compare it with WL's transcript, because there you can get some facts and see how skewed a documentary can be. As a conclusion, I'd say don't waste your money on this, specially supporting it.
Just one last thought on my "summary" title: "We steal secrets" is not a phrase from Wikileaks, it comes from Michael Hayden, former NSA and CIA director, and I think it fits perfectly the American intelligence motto, to steal secrets even from its own law-abiding citizens. This "documentary", just like this phrase, fits strangely well to NSA's narrative of the case, which makes one wonder why the director made so many gross factual errors.