The DC Universe is much like the real world, if you ignore all the tights and capes.
The home of DC Comics, the world is home to the familiar as well as the fantastical. Many elements of popular science fiction - such as artificial intelligence, faster than light travel, and aliens - exist, and yet they haven't radically altered the face of the Earth.
The world is still a relatively grounded place. The existence of the Metagene and Magic both explain superhuman abilities which are well known to the population. The existence of aliens is taken for granted. In short, there's not much which isn't known about to the public - at least in general terms, although specifics are often kept secret for their own good.
The greatest cities in the world are Gotham, a dark reflection of all the worst elements of living in a metropolitan environment, and Metropolis, a more bright and hopeful place. Many of the stories unfold in and around America, although exceptions do exist - particularly with other made up countries and places, such as Atlantis, and interstellar space. For all these wild and crazy possibilities, most people are still focused on old, familiar problems. Love, life, and the pursuit of happiness.
There aren't many universes which have had an easier time integrating into and accepting the Multiverse as the DC Universe.