Yes, I think that Roger Ebert was the greatest movie critic of all time. Evidence to support this theory I think can be found in the fact that he is the best-known movie critic of all time. When people hear the name "Ebert" many people automatically know that name is a movie critic.
He was funny and honest. He would explain his reasons behind the 'thumbs up or thumbs down" responses. He was well known, and well loved and he will be sorely missed. There were many movies I watched simply because the critics were so well done, and on the other hand, I avoided those that were less than praised.
Ebert was the most relatable to the largest audience. He brought people in, he gave more than "I like it" or "I don't like it." The thumbs up/down gimmick he and Siskel put together began being adopted by everybody. It's hard to argue he wasn't the best at what he did, if nothing else he was the most well known.
Yes, I believe Roger Ebert was the greatest movie critic of all time. He gave detailed and in-depth reviews of all kinds of movies. He not only watched commercial, main-stream movies, but appreciated independent, foreign and old-time movies as well. These are all very important in having a full appreciation for movies.