It's always a challenge to say specifically what makes a TV comedy outstanding, but, as Justice Potter Stewart said of pornography 45 years ago, "I know it when I see it." When it comes to "Modern Family," you will, too.

Long on heart, brimming with great characters, smartly cast, expertly written and funny from start to finish, "Family" is the obvious choice for best new fall comedy -- and possibly best series.

If ABC's new two-hour comedy block puts the network on top on Wednesdays, much of the credit rightly will belong to veteran sitcom producers Steven Levitan and Christopher Lloyd. Their new series, with its multifamily approach and semi-documentary form, redefines, updates and invigorates the family-comedy genre. Freed from the speed bumps created by laugh tracks, the show moves smoothly and briskly, with one good line quickly followed by another.

The premiere introduces viewers to three families. Ty Burrell and Julie Bowen play the traditional mom and dad. Burrell takes the role of TV clueless dad up a notch by deluding himself into thinking he is hip and cool. Bowen portrays the mom as a former wild child who now worries her kids will follow her former rebellious path. Their three kids -- a high school cutie, a precocious daughter and a klutzy son, all familiar TV types -- turn everyday parenting challenges into comedic gold.

The second family, a gay couple played by Jesse Tyler Ferguson and Eric Stonestreet, become adoptive parents in the opener. Ferguson's comedy skills were apparent on CBS' "The Class," then obscured in Fox's "Do Not Disturb." Here, and especially opposite Stonestreet, Ferguson realizes his potential.

The third family is a May-December combination played by Ed O'Neill and Sofia Vergara. O'Neill's Al Bundy is one of TV's most unforgettable characters, but this role will let viewers see him in a new light. At the same time, Vergara's character confirms that the former calendar-pinup girl can be a formidable comedy actress, something her previous series suggested but didn't conclusively demonstrate. In this show, she has a stocky young son from a previous marriage.

The premiere's story line leads up to a big surprise, which won't be divulged here. Suffice it to say, though, that the twist creates the potential for even greater hilarity in future episodes. Is the sitcom staging a comeback? If previous ones were this clever, the genre never would have fallen off.

Airdate: 9-9:30 p.m. Wednesday, Sept. 23 (ABC)
Production: Twentieth Television in association with Levitan Lloyd Prods.
Cast: Ed O'Neill, Julie Bowen, Ty Burrell, Sofia Vergara, Jesse Tyler Ferguson, Eric Stonestreet, Sarah Hyland, Nolan Gould, Ariel Winter, Rico Rodriguez
Executive producers/writers/creators: Steven Levitan, Christopher Lloyd
Producer: Jeff Morton
Director: Jason Winer
Director of photography: David Hennings
Production designer: Richard Berg
Editor: Ryan Case
Casting: Jeff Greenberg