I think everyone who knows some about him will have an opinion on him - I'd call him divisive. I'll try to give a relatively neutral rundown - I'm not a historian or researcher on this subject so my knowledge is likely to have holes.
I don't have time to treat this like a dissertation or adding citations, but I'll try to present things as neutrally as I can and then you (or anyone else reading) can decide to further research any of the points as you see fit. I am not the final authority on this, just someone who's dug a little more into this than the average person, and who has no strong feelings for or against the person in question.
He is a political twitch streamer. He ties himself to, and uses the language of, the far left and related candidates. He backs and campaigns for progressive candidates which often raises awareness and donation for them, but the effect seems to be limited - some candidates he backs does well and others do not. He also seems to make plenty of statements that directly contradicts the candidates he backs and campaign for, causing some of them to try to distance themselves from him.
He appears to be well-versed in U.S. electoral politics, media framing, and progressive political arguments, which tracks with his bachelor’s degree in political science and communication studies from Rutgers from 2013. Being a streamer he ends up talking about a lot of related subjects, in which he often has to give off-the-cuff opinions and takes, which can often fall well-short of informed or accurate.
He says his end goal is communism. He got his start as a content creator in his uncle's online news channel (The Young Turks), before later splitting off from them and doing his own streaming business. He is from a very affluent family, personally earns a lot of money and he clearly lives an affluent lifestyle. He claims to thrift for designer clothes but when pressed appears to reference outlet stores and similar. Initially he claimed that he doesn't want his regular thrift stores to get raided by fans, although his fans might be less affluent than him and therefore better served by access to these stores. He has done several very successful charity streams that amassed large amounts of money for good causes. He claims to donate great amounts of money to charities, although the amount of donated money that can be tied to him is very low for his level of wealth, somewhere between 77.000 - 80.000 USD total (0,5-1%) of his estimated wealth, which is 8-14 million USD. While he does not appear to put his money where his mouth is, he does spend some of his time on popular fundraising, which drives a lot of attention to both him and the causes he fund-raise for.
He is often abrasive in his communication, although he will excuse that with passion for the subjects he talk about. He has a large audience that aggressively attacks dissenters or people Hassan expresses dislike for or disagreement with. The harassment from his fan base appears to be significantly above and beyond the norm for the space, and while he comments to the contrary it would be hard to believe that he is unaware of the dynamic between him and his fan base. From what I can tell he has taken no steps towards solving this dynamic beyond disavowing some instances of the harassment, while condoning other instances. He does not appear to have a problem with lying about people or broadcasting random people (even known malicious actors, that he himself states to be malicious) on twitter or twitch if it fits his narrative.
He often breaks the rules of his streaming platform (twitch) but receives special treatment, although I am unsure if that is due to personal popularity or personal relationships with the owner of twitch.
He denies using a shock collar on his dog, but looking at the evidence gathered through old videos, still frames from new videos, and from people who personally interacted with the dog would suggest that to be a lie. I do not know if he still uses a shock collar on his dog since the latest controversy.
As said, feel free to research each of these points, but do be critical of the sources of information and try to just find the actual evidence of what was done or said, rather than peoples' conclusions. He is divisive so when people give their take they usually either dismiss all the criticism and focus on the things he does well, or dismiss the things he does well and focus on the criticism.
Find all the evidence you can and make up your own mind.