He definitely let himself be played by the Russians and used to strategically release information timed to do the most damage to Hillary Clinton. At the least he’s a Kremlin asset, in the same sense that James Clapper observed Donald Trump is a Kremlin asset.
Beyond that, it’s impossible to say. I tend to lean to saying he’s in over his head, partially due to his own personality defects. I think it’s pretty obvious that he has a personal grudge against Hillary Clinton. As someone who’s harshly critical of Hillary Clinton myself, I understand some of that grudge, but it’s important not to let oneself be blinded by one’s grudges.
I also think that Assange ended up provoking the USA far more than he thought he would; I don’t think he believed the US would try to jail him for his political activities. The shock of that doubtless has influenced his antipathy towards the US empire.
I have antipathy to that empire, too, but it’s important to keep in mind just what forces you are aiding in your activism. There are wannabe empires in the world, and just because the US empire has been bad doesn’t mean that the wannabes will necessarily be better.
In the case of China and Russia, all available evidence indicates they will be worse. At least the more open political environment in the USA leaves the US empire significantly more vulnerable to being shamed.