I don't get the manic depressive vibe from Putin at all. Granted, it's not as if I associate with him on any basis, so it's hard to know what he's really like.
That being said, I definitely think he's got some psychopathy going on, as well as megalomania and narcissism. I can't imagine that Putin was unaware of or not involved in the decision to murder a former spy with a nerve agent in a foreign country. This applies to Skripal and Litvinenko, of course, though the former is more worrisome. The polonium tea incident was likely only going to kill its target; the use of Novichok on Skripal and his daughter very well could have injured or killed multiple people. Normal people don't casually accept the possible deaths of multiple people and carry on with that course of action. So yeah, definitely some psychopathy going on.
Megalomania is evident in the way that Putin has stubbornly clung to power, evading term limits and the like. Narcissism is an easy call, as well, given the cult of personality around Putin that exists in Russia. One only has to see just how many shirtless pictures of Putin exist, versus how few for other world leaders.
In any case, while North Korea gets a lot of press, I think Russia and Putin are the gravest threats to world stability. We all laughed at Mitt Romney in 2012 when he pointed to Russia as a major threat, but now his remarks seem eerily prescient. The fact that we have a Putin fanboy as the supposed leader of the free world only means that Putin feels comfortable doing whatever the hell he wants.
Definitely not a good situation. I think the next few years will be a rough ride as Russia continues to flex its muscle on the global stage.