I'm glad I didn't see the trailer first; I would've expected an entirely different movie.
Senses of Cinema says it "is one of Ingmar Bergman’s most important and most perfect films, marking a high point in his distinctive formal experimentation". filmref.com describes it as "an examination of emotional isolation in a world without God - where salvation lies in human connection." Roger Ebert has it on his list of great films. Only the Cinema says,
the film is about much more than the absence of faith: it is about the myriad ways in which communication can fail, the ways that speech and language can drive people apart rather than bringing them closer to mutual understanding