Public opinion was a divided house. I am sure he had whole-hearted supporters being a Democratic hopeful, and followers too. His men recognized him as their leader and were grateful for his attention on them. That could not ever be won in the public sentiment unless he had won the election of 1864, and then one can only guess what his rating might have been. Good question, @MikeyB.
Lubliner.
The newspapers hailed him as the American Napolean. Unfortunately, after the news media puts you on a pedestal, they then start to see if they can knock you off it.
Good question. My guess is that his popularity had ups and downs based upon events. As @Andy Cardinal noted Ball's Bluff was embarrassing, I imagine the failure of the Peninsula campaign as well. However during Maryland campaign when McClellan entered Frederick the crowds rushed him with women holding out their babies to him. I think in the post 2nd Bull Run panic he was genuinely seen as savior.