What are the major themes and concerns about postmodernism?
One of the historical events to come out of the Postmodern era has been globalism. And, with this event, the concept of identity has become more free but also more fragmented. For example, it is now more common to see a person from a conservative religious or cultural background wearing a Che Guevara t-shirt, listening to Outkast and reading Karl Marx. While this has been wonderful for sharing ideas between people and cultures, it reflects one of the concerns of postmodernism which is a fragmentation of identity. In other words, postmodernists criticize neat, clear-cut, identities because they are cliche or because such identities support existing power structures (which tend to oppress certain groups). So, the freeing up of the categories of identity has been just that: freeing. But with it comes the fragmentation and difficulty of finding a way to fit in when these pre-established categories of identity are dismissed in favor of more versatile concepts. Despite the confusion with identity, this global cultural sharing has certainly been worth it.
Another theme of postmodernism is self-reflexivity. This is discussed in the previous answer. In postmodern literature and film, many people have experimented with structure, non-linear narratives (Pulp Fiction), form and content. A professor of mine once described postmodernism as "tying a tie while describing how you are tying it." That is to say that self-reflexivity is thinking about, and calling attention to, what you are doing while you are doing it. This is to give attention to what, why and how we do what we do. Reality television is a fair example of this blending between art and life. (However, much reality television is scripted, so the term "reality television" is actually a misnomer.) This blending (like the fragmenting/blending of identity) has been happening in the arts and in real life. Think of how many people have smart phones; everything is documented. These people archive what they are doing while they are doing it. They make movies of their lives; a blending of art and life, of the organic and virtual. In the end, this blending of categories of identity, art and life, non-linear and linear, these are all about breaking boundaries. This is creative and liberating but can be confusing. Thus, the term "postmodern chaos" has been used often to describe this kind of conscious restructuring of our lives.
The major features of postmodernism are experiment in narrative techniques, form, language, expression, rather than content, social milieux, or psychological characterization—the possibilities and limitations of written language, the exhaustion of the signifier/signified relationship. James Joyce is a good representative, as are Samuel Beckett, Jorge Luis Borges, and Kurt Vonnegut. Postmodern literature does not tell a story so much as expose the artificiality of doing so. It is a questioning of submerged assumptions about literature, about philosophical underpinnings that had pervaded literature up to modernism. The question began with the examination of language by Nietzsche, Hegel, and structural linguists, and its existential base is founded on questioning the nature of humanity, especially the notion that humans have an “essence” not possessed by animals. There are also political and historical ramifications, and some sociologists see it as a reaction to the chaos of a post-world-war world.