Debuting at 10 tonight on ABC is a noble experiment. “Once and Again,” a limited series which airs until “NYPD Blue” returns Nov. 9, tells the story of two people yearning to break out of their ordered existences, to once again find love.

In the premiere episode, viewers are introduced to Lily Manning (Sela Ward, “Sisters”), who’s been separated from her horndog husband, Jake, for eight months. She’s raising two daughters, 14-year-old Grace and 9-year-old Zoe.

Then there’s Rick Sammler (Billy Campbell, “The Rocketeer”), who’s been looking for that right person since his divorce three years ago. He shares custody of 16-year-old Eli and 12-year-old Jessie.

They spy each other across the car-pool lane at school, and later meet in the school counselor’s office. Two stammering phone calls later, and they’re off on their first date. They click, but forces within each family buffet their budding romance.

Ward and Campbell bring all their characters’ insecurities to life, both through the body language and by breaking down the fourth wall, revealing their innermost thoughts. It’s a device that can be overdone, but it works here. In a medium overrun by youth, it’s a pleasure to find such a pair of intelligent, nuanced adult characters. At the same time, the series doesn’t slight the younger characters, and their concerns about their parents dating again.

Not surprisingly, “Once and Again” is the brainchild of Edward Zwick and Marshall Herskovitz, who also created “thirtysomething” and the gone-too-soon “My So-Called Life.” The new series combines the best parts of those two dramas into a whole that sells nobody short.

“Once and Again” faces the daunting task of taking off in six short weeks, to do well enough that ABC will move it to another time slot in January. Since it’s seeking the same type of viewer as “Judging Amy,” it seems likely that only one of those newcomers in the time slot will survive. And that one should be the more well-rounded “Once and Again.”

Tonight’s other two new entries, both reputed comedies, don’t have as much to offer. First up is the animated comedy “Mission Hill,” debuting at 9 p.m. on WB before moving to its regular slot of 8 p.m. Fridays. In the premiere, one character comments, “Oh, God! Not another animated series.” Viewers of “Mission Hill” will soon be saying that, too.

In the new show, Andy French is a would-be cartoonist working as a waterbed salesman. He lives in a Mission Hill loft with two loony roommates, his old friend Jim and flower child Posey. Then Andy’s parents announce they’re moving to Wyoming. The upshot of this is that his overachieving younger brother, Kevin, and his disgusting dog Stogie move in with Andy.

“Mission Hill” has a good pedigree, as it is created by Bill Oakley and Josh Weinstein, Emmy-winning producers of “The Simpsons,” and is voiced by, among others, Wallace Langham (“The Larry Sanders Show”) and Vicki Lewis (“Newsradio”). But its message is hardly anything novel. Kevin seeks to enjoy his newfound freedom, but discovers that he has to be true to himself. Andy finds out that he loves his brother more than he lets on. It’s far too warm and fuzzy to be an effective satire on youth culture.

At least it’s OK for cartoons to be two-dimensional. But the other new comedy, the live-action “The Mike O’Malley Show,” focuses on the hoary but dubious TV staple: the manchild who is a commitment-phobe. In a vehicle for yet another comic, Mike O’Malley (his character is named after him) lives in frat-house splendor with a lower life form known as Weasel, unwilling to grow up.

In the opener at 9:30 on NBC, Mike is aghast that his best friend Jimmy is again considering marrying Marcia, who left him at the altar once before, and that Jimmy wants him to repeat as best man. Being the semi-adult that he is, Mike finally makes it to the reception, and uses his best-man’s toast as a feeble attempt to reconcile with his old girlfriend, who left because Mike was content to drift in their relationship.

O’Malley the character also talks directly to the camera in this series. This approach can work, but only if the character has something revealing or poignant to say, which Mike generally doesn’t. Neither does his sitcom.