How will we ever live without Lost? ABC is confronting that dilemma head-on this season, preparing for a Lost-free future—the groundbreaking show begins its final season this winter—by dipping back into the science fiction/fantasy well with two spectacularly ambitious series that couldn’t take more different approaches to asking “what if.”

FlashForward has been on the air since late September, but still feels in many ways like it’s just getting started. This existential thriller asks big questions about fate and destiny in the wake of a worldwide blackout in which everyone gets a glimpse into their future, for better or worse. (The good news is that the show’s immediate future is assured, having been renewed through the end of the season.)

V, which launches a four-episode “pod” Tuesday night (8/7c) that picks back up in the spring, is far less oblique and, judging by the fast-paced pilot, is more immediately satisfying and suspenseful. A rip-roaring twist on the alien-invasion scenario, this is a reinvention of a popular ’80s miniseries-turned-series.

It doesn’t go much deeper than “Who can you trust?” paranoia—focused on the coolly sinister, sweet-talking “Visitors” with their advanced technology and cloaked reptilian innards—but V nicely exploits the unease in a world of next-door terrorist cells and mob-mentality zealotry.

It’s doubtful either show will have the pop-cultural impact of Lost, a true landmark that broke all the rules and continues to confound and astound. Unlike Lost, which took several seasons to become hopelessly complicated, FlashForward was murky from the start. Some major characters, including Dominic Monaghan's enigmatic Simon, are only now being introduced, so who can predict where the show is ultimately headed—except toward April 29, 2010 (a Thursday, by the way), the date of the flash-forward. My biggest problem so far is that the epic nature of the premise has not been sustained in the weekly episodes, which feel too narrowly focused on lackluster FBI hero Joseph Fiennes and those in his immediate orbit. It’s still early, but the clock’s ticking.

I’ve only seen the V pilot—several times, actually, each time yearning to see more—so I can’t be sure it will hold up on a weekly basis, either. As enjoyable and exciting as the pilot is, it’s undeniably more simplistic than either Lost or FlashForward in its us-vs.-them setup. But I was instantly seduced and hooked by its lavish production values, the immediately gripping storyline and a strong cast led by Elizabeth Mitchell as the required FBI skeptic, The 4400’s Joel Grestch as a conflicted priest who joins her in the resistence and Scott Wolf as an ambitious TV reporter who makes a deal with the otherworldly devils to gain access to Morena Baccarin as the unnervingly alluring leader of the V’s.

V may not initially dig as deep as FlashForward, but there’s a juicy urgency to all of the interpersonal and intergalactic melodrama, with plenty of action and surprising reveals.

Will either show lessen the blow of Lost’s departure? Probably not, but I give ABC a “V” for valiant effort.

In other TV news, HBO premieres the two-hour documentary By the People: The Election of Barack Obama tonight (9/8c), marking the one-year anniversary of the historic election night. Here is part of my report on the film from when HBO presented it to critics last summer as part of the TCA critics’ press tour.

Actor Edward Norton produced this unusually intimate fly-on-the-campaign-trail account of Barack Obama's unlikely rise from underdog to front-runner. Filmmakers Amy Rice and Alicia Sams spent more than two years getting close to the family, the advisers, the organizers and volunteers of the campaign. Rice: “We really didn’t have a firm idea of what this movie was going to be or that he was going to run for president.” Norton said the original concept was for a “political diary,” and he imagined the project having a six-year timeline, never dreaming Obama would actually run for the White House so soon.

They gained early access because “at the time, he wasn’t a candidate. They weren’t trying to insulate him. They were in some sense trying to elevate his profile,” said Norton. “We were lucky to start forming the relationship with them before it became a much more guarded affair.” As the campaign grew, “it went from a very innocent time to a very scheduled program,” said Sams. Even so, the movie presents a number of candid moments of Obama, Michelle and their daughters. (One amazing shot captured by Rice shows a tear falling down Obama’s cheek as he made a speech on Election Eve shortly after his grandmother had died.) But the film is just as enraptured with the idealism and sense of purpose of the young staffers who are often overcome with emotion as the enormity of their mission becomes clear. “The film was a portrait of the movement that elected [Obama] as much as it was a portrait of him,” said Norton.

The emphasis is less on War Room-style political process than on the grass-roots trajectory that catapulted this most unlikely and improbable candidate to the White House. “We didn’t set out to make a campaign film, but I think at a certain point it became clear to us that it was a document of how this momentous piece of history was achieved from a certain perspective,” said Norton. “Whatever President Obama goes through, whatever the struggles and the ebbs and flows of success or failure in his presidency, I don’t think anything will ever diminish the significance of the achievement of his election.”