The other day, a colleague was discussing a basic cable series. While the show wasn’t completely satisfying her, she nevertheless referred to it as being “better than a network drama.”

The idea that “network drama” has become in certain quarters a kind of generic term for “mediocre” reflects a sobering reality: At the very moment when TV comedy appears to be regaining ground as a commercial force, the network drama suddenly looks shaky.

The reasons are varied, but the main one — and key source of qualitative demarcation between broadcast and cable — hinges on a single factor: The power — and indeed, desire — to surprise.

Nothing exemplifies this better than alternate versions of one of the fall’s biggest dramatic bets, Fox’s sci-fi adventure “Terra Nova.”

In the one-hour pilot previewed to the press months before the show’s debut, a key plot point involving the central couple’s third child was held back as a shocking revelation. Yet in the revised two-hour premiere that actually aired, everything about that storyline was immediately made explicit, and the sequence when the frightened kid is yanked out of a backpack played like a mere afterthought.

True, it’s just one example, but it’s indicative of the prevailing mindset: Some execs have come to view acceptable ratings and critical acclaim as being mutually exclusive. After a stretch where programs like “Lost,” “24” and “Desperate Housewives” consistently delighted viewers with twists, the networks seem far more content to replicate a working template.

Granted, that isn’t always a bad thing, and a show like CBS’ new “Person of Interest” isn’t without its simple, cathartic charms. There are also obvious scheduling benefits to programs that don’t rely on the kind of sweeping serialized plots that have scant repeatability on air.

Nevertheless, there’s no comparing those self-contained experiences with series like AMC’s “Breaking Bad” — perhaps TV’s most unpredictable franchise — and now “The Walking Dead,” or pay cable fare like “Boardwalk Empire,” “Dexter” and Showtime’s new drama “Homeland.” Even cable programs not perceived as breakout hits, such as TNT’s “Southland,” have garnered admiration from those fans who do watch by delivering highly unexpected developments.

Instead of taking genuine chances, the networks this fall mostly mimed the appearance of risk. Thus, we got two 1960s-era dramas, “The Playboy Club” and “Pan Am,” which, once you got past the concepts, unfolded like highly conventional soaps; and “Terra Nova,” whose spirit of adventure stemmed more from its cost than its content.

For that reason alone, the networks — and particularly TV’s creative community — should be heartened by strong initial ratings for ABC’s fairy-tale-themed series “Once Upon a Time.” If broadcasters needed some current validation that they can play beyond the procedural sandbox, there it stands.

At least, for now — and within that disclaimer lies another complication. As was noted in a recent TV Guide piece, one thing networks covet is the potential for longevity. “Sure, nice pilot,” they’ll say, “but we’ve been burned by those before. What we really need to feel comfortable is a sense you can do this over multiple seasons. Remember ‘Heroes?’ ‘Cause we do.”

By contrast, a show like “American Horror Story” looks as if it’s going to fly apart in practically every episode. Yet enough viewers have been transfixed by its dysfunction to merit a second-season renewal from FX.What the major networks really need is a happy medium: Programs that can startle viewers without being such high-wire acts as to make long runs unlikely. Even “Lost” ran into that buzz saw, but the producers wisely changed the rules by setting their own end date.

As FX prez John Landgraf told TV Guide, the broadcast nets “can succeed with a variety of comfort-food shows if they’re executed well. But I think it’s harder to stand out with that kind of programming.”

“Once Upon a Time” proves the elder networks can still stand out amid all the clutter. And the season isn’t over, with a few other daring bets — including ABC’s adventure-mystery “The River” and NBC’s musical “Smash” — due in 2012, offering hope for more happy endings.

Even so, after the fall’s sluggish start, it’s going to take the magic of surprise — as well as proof “Once” isn’t another one-trick pony — to rouse network drama from its creative slumber.