Metatropolis is a fascinating book. There are a few different things that make it so. Its five novellas, all by different authors, are set in the same world, a somewhat near-future Earth after some kind of fossil-fuel crash, a dystopian world that's working hard to make things even better than before (so, an optimistic dystopia). Among the five stories the world-building is consistent, so we end up with a world that, in terms of internal consistency, could have been invented by a single author, but is instead richer for the variety of voices and viewpoints that each author brings to the collaboration.
The world that we end up with is an interesting one: the rise of transnational corporations and the massive disruptions in resource allocations have all but neutralized the power of traditional nation-states. Meanwhile, society and economy have evolved to a point where old understandings of geography have ceased to have any authority. The definition of "urban" is constantly in flux, and what it means to live in a city has changed as well. Living in a city entails deep entanglement with and quick access to a great variety of social networks, but the ways in which technology changes and is used can have a massive impact on what cities look and feel like. Two examples in Metatropolis serve to illustrate the point: first is the city of Cascadia, which is an urban corridor stretching from Vancouver to Portland (Oregon) but exists side-by-side with a vast community of eco-anarchists living in harmony with nature. Moreover, this Cascadia has an "open-door" cross-citizenship relationship with a number of other urban areas around the world, including New St. Louis, Shanghai, and a few others. Jay Lake's story "In the Forests of the Night" builds this little world in great detail. The other example is "Cilenia", which is not a physical place but is indirectly linked with real-world places. It's hard to explain this augmented-reality world without depriving the reader of the pleasure of discovering the relationships between Cilenia and the real world -- just read Karl Schroeder's "To Hie From Far Cilenia"! You can read about Detroit and New St. Louis in the other stories.
The world-building is the main attraction of this book; indeed, much of its significance lies in the fact that it presents a clear-eyed vision of a direction that human civilization could take in the next half-century or so. It makes readers ponder just how their relationships with people and places are defined; it deconstructs old concepts of these relationships and reconstructs them, at times, brilliantly. On this count, Jay Lake's and Karl Schroeder's stories are the shining stars of this book; and, being first and last (respectively), they establish and leave a powerful impression of the world to come.
Besides the world-building, the quality of writing in these stories is top-notch. While Elizabeth Bear's and John Scalzi's stories are a little more lightweight in this respect, eschewing lyrical style for clear character-building and plot-presentation, the other three stories are a pleasure to read for anyone who appreciates dense, prickly, and/or singing prose. Jay Lake's story is the most beautiful in this regard, taking many of its cues from William Blake's poem "The Tyger" and aspiring to the sublime lyrical quality of that work. Tobias Buckell's story is the kind of action-adventure that uses the shape and texture of its words to bring you along for the ride (the literary equivalent of a Paul Greengrass film, I think, if you replace "words" with "cinematography"). Finally, Karl Schroeder's story is the kind of sci-fi exploration story that you can't put down because you're constantly working your way up to the next great revelation.
All in all, I highly recommend this book to any fan of science fiction. Everything that makes old-school anthropological sci-fi great is here (world-building, social speculation, and intricate prose). You'll also find that the authorial voices, in their variety, actually complement each other to build a world that you really want to see more of. Read it, enjoy it, and ponder it.