The first Steampunk anthology, edited by Ann and Jeff Vandermeer, still laboured under the definition of Steampunk as a literary genre. It deliberately set about reprinting stories by the pioneers of that literary genre, such as Michael Moorcock, James Blaylock, Paul Di Filippo and Neal Stephenson. These works were prefaced by a trio of essays charting the genre's development through literature, film and comics.
Steampunk II, edited by the same, engages Steampunk post-genre. The aforementioned gulf is that of its development from a genre to a scene, on one side of which are the older authors whose writings shaped a literature and on the other are the newer authors writing to a subculture. Not only are the stories different - including a number of what the Vandermeers call "steampunk tinker" stories that are literary paeans to the scene's DIY fashionistas - but the essays moreso reflect this transition.
The Vandermeers begin with a crude overview of Steampunk that is only as accurate as necessary for a scene that neither wants nor needs a comprehensive history. Well, unless you're Mike "Steampunk Scholar" Perschon, who asked to republish the History of Steampunk piece deleted from this weblog (and got one of my tiresome rants in the process). The only relevant historical essay was that submitted by Jake Von Slatt. As his greatest invention is the Steampunk scene itself, he speaks credibly when he declares that "Steampunk is part of this Maker Movement..." The idea of Steampunk represented in this anthology does owe more, as he implicitly suggests, to the existence of Radio Shack and Make Magazine than to a genuine interest in the Victorian Era or Scientific Romances. At this juncture, I'm not even sure why he chooses to belabour any kind of idealistic, romantic fantasy about how "The Victorian era was the last time that the typical high-school-equivalent education... gave the graduate all of the tools that he or she needed to understand the technology of the time." 
Gail Carriger attempts to link the reading of Steampunk fiction with the wearing of Steampunk costumes, to irrelevant effect. She concludes her essay with what is supposed to be an affirmative note, but in the course of it articulates the fact that fashion scene rose independently and has nothing to do with the Steampunk genre. Following Carriger's and Von Slatt's pieces, there is a "roundtable interview" on The Future of Steampunk in which various and sundry of the scene's Internet celebrities comment on how they would like to see it further overwritten with their own values and interests.
The included fiction is a grab-bag of established authors slumming out a few Steampunk stories and a few aspiring ones who owe their success to writing for the scene. Of greatest value for readers who actually enjoy Victorian-Edwardian Scientific Romances is the first English translation of Danish author Vilhelm Bergsøe's 1870 short story Flying Fish 'Prometheus' (A Fantasy of the Future). "Steampunk III: Steampunk Revolutions" is not in store, according to the Vandermeers, but an anthology translating and/or reprinting the lost and out-of-print volumes of Scientific Romances of the 19th century would be a welcome new course after Steampunk II.