Ares Express - Ian McDonald
This is a big, colorful, exuberant adventure story, with the energy and sense of mission of its seventeen-Earth-year-old protagonist; it has inventiveness in plenty, and rejoices in it.

We are on a Mars that's been made habitable, but by art not evolution. Implausible things happen constantly, in fact many events seem like magic, but it's really Sufficiently Advanced Technology. AIs that can manipulate the quantum structure of the world shape reality nearly as they wish, but I imagine there must be limits on their power; after all, things are not quite chaotic, they do have a certain skewed logic, and internal consistency within local patches. The artificial nature of the world might explain the oddly retro nature of the decor -- pop culture seems taken straight from various parts of the 20th century but especially the 1950s (global, though, not just U.S.) It could reproduce chunks of the past if it's implanted rather than evolved. That would (sort of) explain the presence of the Glen Miller Band, which seems to be the actual Glen Miller Band.

I know the author has some thematic reasons for what he chooses to write, he's not just having fun -- but he's having fun too. The whole thing is extremely self-conscious about being Story (the main character ticking off when she goes through the major plot arc points), which may be a reflection on what things would be like if we really could manipulate reality by its quantum structure.