No. 1 - Darkness on the Edge of Town (1978)
For the first time, Bruce Springsteen took the characters of his narratives national instead of just remaining along the Jersey shore. From the powerful, full sound of Born to Run, the artist wanted a stripped-down record. While still very much a rock album, and there are some elements of punk involved, there are more Americana principles both in the lyrics and the instrumentation. The characters are hard-worn by life but not ready to give up.
This is a theme that Springsteen would become well-known for and still continues. Possibly his best-known song, "Born in the USA," is partly about a protagonist whose brother was lost due to the war in Vietnam. Many conservatives have misunderstood this to be a pro-American hymn when it is anything but.
Such is the case with many of the tracks from Darkness on the Edge of Town, especially the amazing "Badlands." One reason that the album was inspired by the novels of John Steinbeck and the films of John Ford is that the characters in those books and films are much the way Springsteen feels about American life: Things are not as easy as some think they should be and one has to fight to survive.
To be sure, of all four of Springsteen's first four albums, this may be the least easy to listen to because of the themes. Musically, it's fully formed, however, and strong. He would leave some of the hardness behind in the 1980s where while his popularity grew he also became a bit more poppy. At least, after 1980's The River, that is.