When the cover art for "BioShock Infinite" was revealed a few months ago, it produced an outcry from fans. They felt the straight-ahead image of a muscular man holding a gun, looking no different from the cover template of mindless shooters like "Call of Duty," didn't do justice to this brainy, beautiful series. Little did they know how fitting the cover would prove to be. "Infinite" is as good an action game as you'll play all year, but the thing that makes the series so special -- its thought-provoking and miraculously unannoying exploration of politics -- is all but missing this time around.

2007's BioShock and 2010's "BioShock 2" took place in Rapture, a secret city at the bottom of the ocean. This gleaming, Art Deco metropolis surrounded by water was the creation of an Objectivist who wanted freedom from God and government. The first "BioShock" looked at a society built on radical individualism. The second, taking place after Rapture is under new management, so to speak, looked at a society built on radical collectivism. "Infinite," a prequel set in 1912, and infused with the aesthetic of the era's World's Fairs, takes place in another secret city, this one not below the sea but above the clouds.

Columbia, which floats by a miracle of quantum science, is built around a civic religion of American exceptionalism in which George Washington, Thomas Jefferson and Benjamin Franklin form a sort of Holy Trinity. It's a neat idea, but it's never fleshed out into a comprehensive or comprehendible belief system, so you're deprived of the joy of pondering its vision for how human society should run. More fundamentally, the game doesn't seem to respect any of the viewpoints it presents. Columbia's leaders, presumably meant as stand-ins for the Tea Party, are caricatures of jingoism, greed and racism -- there's even a John Wilkes Booth Memorial -- while the proto-Occupiers known as the Vox Populi are caricatures of virtue -- until, for no reason I can figure out, they turn absolutely evil. The first two games looked at their subjects with earnestness, curiosity -- even wonder -- but "Infinite" goes out of its way to arrive at moral equivalency, teaching us the misanthropic lesson that people of all political stripes can be bad. Oh, now we know.

It's hard to find an intellectual or emotional entry point into the game. If there is such a thing, it's Elizabeth, the girl your character is rescuing, who accompanies you for most of the game. "Infinite" marks the only successful attempt by an action game to give your player a companion. Elizabeth aids you in fights -- but, crucially, always at your direction, so it never feels like the game is playing itself. "Resident Evil 5," even "Fallout 3," have a lot to learn from this game.

'BioShock Infinite'
» System: PS3, Xbox 360, PC
» Price: $59.99
» Rating: 4 out of 5 stars

In terms of pure gameplay, "Infinite" doesn't reach the heights of "BioShock 2," whose masterstroke was inverting the action so the focus was on playing defense, but the combat is more dynamic than anything "BioShock" has done in the past. Credit the game's free-wheeling fights to the addition of the Skyline system. Columbia is connected by a network of rails snaking through the sky, and your character can latch onto them, holding on with one hand and shooting with the other. Skyline transforms regular firefights into almost literal roller coaster rides as your character zooms around the floating buildings, blasting away. A sequence in which you're hounded by a zeppelin, hopping on and off the rails to fire from various locations, is the single most spectacular piece of gaming in recent memory.

"Infinite" is philosophically muddled, and the "BioShock" mystique, cultivated in the dank, leaking hallways of Rapture, dries up in the sunlight of this squeaky-clean Emerald City in the sky. But even if "Infinite" is a letdown by series standards, it's an outstanding action game, and as always, I can't wait to see what's next.