Yes, it definitely is, and I believe that it is among the best.
The movie has a very unique greatness. It may not be as important and revolutionary as Citizen Kane or The Godfather, and I do not deny it. However it has some things that few movies have ever had:emotional impact, deep life lessons, deep underlying themes and symbolism that just wait for the audience to explore. The movie itself is a very realistic metaphor of a man's life. Fictional stories sometimes give a very decent account of our real world. On every rewatch, I find something new in the movie.Well, I think I cannot say further. I do not want to impose my thoughts on you. You should see it yourself and feel its greatness yourself.
I would like to say some more words: The concept "The greatest movie of all time" does NOT exist. This movie may be number 1 in my opinion, but some others may not enjoy it as much, it's their point. "The greatest" is a movie which NO ONE can hate, which,well, does not exist.
Hope I helped!