What can I say that hasn't been said before about this film? Probably nothing, so I will say what has already been said.
"How this pretentious movie manages to not be pretentious at all is one of the great accomplishments of 'Persona'". John Hardy, IMdB
"[Persona] was not the first shot in a revolution, it was the second shot. It sealed the revolution" Paul Schrader, Criterion Collection interview
"Who is she? Who is anybody? What is real?" Roger Ebert. 1967 review
And the last one, also from Paul Schrader (discussing the change Persona created in the language of cinema):
"It was part of that glowing moment where movies all-of-a-sudden had a higher quality... It was as far from mass entertainment, and yet, it entered into the bloodstream of high-culture, and eventually culture period... You could not pretend that Persona did not exist. It changed everything."