There’s so much to savor about “Boardwalk Empire” — Martin Scorsese and “The Sopranos” writer Terence Winter’s sprawling look at Prohibition-era gangsters in 1920 — it’s hard to know where to begin. One can luxuriate in the atmosphere, or admire the scintillating cast — a shrewdly assembled collection of talented not-quite movie stars, among them Steve Buscemi, Kelly Macdonald, and four Michaels: Shannon, Stuhlbarg, Pitt and Kenneth Williams. As for the story, it’s been a while since such a sweeping, epic backdrop has been put to better use. Having notoriously missed out on “Mad Men,” the mantle of cable’s next great period piece belongs to HBO.

Expectations were certainly sky-high for “Boardwalk,” but the producers have risen to meet them — in a series that grows richer, deeper and more absorbing with each of the six episodes previewed. And while that might not translate into enormous ratings, using HBO’s scorekeeping system — which includes critical acclaim and awards recognition — the pay service should be clinking glasses all around.

Set in Atlantic City at the onset of Prohibition, the 12-parter — enormously cinematic in its look and feel — focuses on real-life figures, albeit in a manner that seems unconstrained by absolute fidelity to history.

Buscemi occupies the center as Enoch “Nucky” Thompson, a political shaker and mover who also happens to earn a pretty penny running illegal booze. In this endeavor he’s aided by utterly corrupt police chief Elias (Shea Whigham), who conveniently happens to be his brother.

Nucky’s circle of contacts includes several higher-profile crime names, such as Arnold Rothstein (Stuhlbarg), a young “Lucky” Luciano (Vincent Piazza) and a young thug named Al Capone (Stephen Graham). He’s also taken under his wing Jimmy Darmody (Pitt), who returned from World War I with a weary, far-away look and a take-no-prisoners attitude.

Buscemi’s anchoring role notwithstanding, “Boardwalk” is really an ensemble piece boasting an extraordinarily rich array of characters. They include Macdonald (“No Country for Old Men”) as a struggling Irish immigrant who comes to Nucky seeking help; and Shannon as the FBI agent assigned to stop the flow of illegal liquor.

History buffs will inevitably nitpick some of the language idioms, perhaps, but the program is impeccable in its detail and establishment of place and time — such as a throwaway reference to Civil War veterans nodding off during an annual dinner.

The setting provides license to incorporate enough violence, sex and nudity to ensure pay-cable subscribers get their money’s worth and then some, while still managing to feel organic in its use. The camera also moves in a way that betrays Scorsese’s touch (he directed the pilot), without distracting in any way from the story.

This is, quite simply, television at its finest, occupying a sweet spot that — for all the able competition — still remains unique to HBO: An expensive, explicit, character-driven program, tackling material no broadcast network or movie studio would dare touch.

The closest precedent in tone, perhaps, would be director Sergio Leone’s “Once Upon a Time in America,” albeit tantalizingly teased out into episodic form. It’s a period we’ve seen too little of, adding a sense of discovery to the program.

Despite the lusty pleasures of “True Blood,” true HBO acolytes have been a trifle nostalgic since “The Sopranos” faded to white. For those wondering when the channel would deliver another franchise to definitively put it on top of the world, Ma, the wait is over: Go directly to “Boardwalk.”

Boardwalk Empire

  • Production: Filmed in New York by HBO in association with Leverage, Closest to the Hole Prods., Sikelia Prods. and Cold Front Prods. Executive producers, Terence Winter, Martin Scorsese, Tim Van Patten, Stephen Levinson, Mark Wahlberg; co-executive producers, Eugene Kelly, Lawrence Konner; supervising producers, Howard Korder, Margaret Nagle; producers, Rudd Simmons, Rick Yorn, David Coatsworth; director, Scorsese; writer, Winter; based on the book by Nelson Johnson.
  • Crew: Camera, Stuart Dryburgh; production designer, Bob Shaw; editor, Sidney Wolinsky; music supervisor, Randall Poster; casting, Ellen Lewis. 70 MIN.
  • Cast: Enoch "Nucky" Thompson - Steve Buscemi Jimmy Darmody - Michael Pitt Margaret Schroeder - Kelly Macdonald Agent Nelson Van Alden - Michael Shannon Commodore Louis Kaestner - Dabney Coleman Elias Thompson - Shea Whigham Eddie Kessler - Anthony Laciura Al Capone - Stephen Graham Angela Darmody - Aleksa Palladino Arnold Rothstein - Michael Stuhlbarg "Lucky" Luciano - Vincent Piazza Lucy Danziger - Paz de la Huerta Mickey Doyle - Paul Sparks Chalky White - Michael Kenneth Williams Gillian - Gretchen Mol With: Frank Crudele, Greg Antonacci.
  • Music By: