The documentary collects a huge amount of information about Nisman (his life, his jobs, his family, his friends, his contacts and so on). Almost every friend or contact speaks out and tell what they think.
The documentary is quite objective, which allows the viewer to reach his own conclusion. It's not propaganda of any kind.
You can have your own opinion about what happened with Nisman (whether it was a murder or a suicide - in my opinion, it seems pretty obvious), of course... but you can't say this documentary is biased.
Finally, even after seeing this documental one question still remains to be answered: who benefited after his death? Who didn't?