Hog has recently received some changes that nerfed his hook combo and buffed his fire rate and magazine size. These changes may seem like unjustified nerfs but they're not. Let me explain why these changes were necessary and why they're not going to make Roadhog completely unviable.
I'll start by clarifying that Hog wasn't overpowered. His pick-rates were fine. His pick-rates in the pro scene were average and his pick-rates in GM were only slightly above that. The devs knew he was balanced, so they didn't nerf Hog, or at least they didn't try to. They tried to change his play style.
His playstyle was changed because he wasn't fun to play against. There is no counterplay to being hooked by a flanking Hog. He was meant to punish bad positioning. But when he was so widely used as a flanker he just punished being positioned. You could be anywhere and have a Hog solo kill you from behind to initiate a fight. There is no counterplay to that.
Roadhog was meant to be a hero who stayed behind the Rein shield and killed anyone who badly positioned themselves. And after these changes he will be played like that because he needs his team to finish off hooked enemies now. So no more flanking Roadhog.
A lot of people are saying that Hog is an unplayable troll pick now, but that seems to happen every time a hero's nerfed, and most times, those people have been wrong. I'm honestly not sure if he's viable like this though, they may need to buff more than just Hog's fire rate and clip size to compensate for nerfing the hook combo. But don't just assume he's unviable in every situation. We can't be sure how these changes will impact his viability yet. All we can do is wait and see how he plays when everyone's used to the changes.