I've been told in another comment that ever since the cancer stuff he's been really nice. I haven't kept up with him too recently, so I wouldn't know for sure, but something like that would definitely change you in some way.
There were a lot of times where he would make out like only his opinion mattered, sometimes during videos talking about people or direct fan interaction. His whole deal with Riot Games about his referral stuff (Which I agree with him on, just not the way he went about it).
He could seem elitist or abrasive at times. It seems like a small thing, but there was a point where he kept going on and on about how Cho'gath (If you're familiar with League of Legends at all, back when he did a lot of League content), was more effective if itemized his way and not the conventionally accepted method and people couldn't tell him otherwise because his mind was set on being different (There were many reasons he used which didn't make a lot sense in context).
Some of his twitter stuff he was up in arms about before, but this was a good while ago now. The way he talked about some of the events he had been to as well.
Quick to give harsh criticism to almost anything but he wasn't very good at taking even constructive criticism even just in comments on videos and stuff.
The kind of sense you can get from a person based on small things like these probably don't come across too well as an argument, but first impressions do last a long time, and these were the kinds of things I saw from him.
Don't get me wrong, he has always made good content, and he definitely shows his knowledge in them, there are just some personal things that leak out and/or are expressed in some of those areas that used to not give me an appealing look of him outside of the content.
I mean I think he was aware of this himself on some level, after all he did call himself "The Cynical Brit"