John Stewart’s material got old to me pretty quickly. Like the OP said, he’s not wrong, but it’s just depressing how screwed up the media and politics are, and I don’t need to see that presented to me every single day.
Jon Stewart is the only news show I watch for US American news. 
Got old fairly fast for me. When interviewing guests who either don’t agree with him or whom he personally loathes he relies far too much on the audience cheering and hollering to get his point across. That’s inherently weak in my opinion.
He has his moments though and I’m glad he’s on as it’s always fun to watch now and then.
I don’t think he does, actually. He lets them cheer usually, but he has told them to quiet down on occasion. I agree, though, it’s incredibly unfair for one side to have a cheering section and the other not, and I wish the audience would show a little more decorum.
Optimally, he’ll attract more folks who haven’t already made up their minds or who are unexposed to media criticism, and will have an impact on them. You can’t sway those who are firm in your belief, but there’s a lot of people out there who don’t even stop to consider the media and how it works. I wonder, though, if he’s gaining audience or if he’s peaked.