Some expected hits have tanked, while certain overlooked shows have stood out. Among the biggest disappointments have been NBC's 'The Playboy Club,' ABC's 'Pan Am' and Fox's prehistoric drama 'Terra Nova.'

The hot stars on the TV screen this fall were supposed to be Playboy bunnies, Pan Am stewardesses and angry dinosaurs.

Instead the winners were broke waitresses, snarky suburbanites and Snow White.

Welcome to the 2011-12 television season, where the costly shows that were supposed to be hits tanked and the ones that prognosticators had overlooked turned into ratings gold.

Among the biggest disappointments have been NBC's short-lived "The Playboy Club," ABC's "Pan Am," which is struggling to stay airborne, and Fox's prehistoric drama "Terra Nova,"which may end up going extinct in its first year.

"Those shows got a lot of buzz and attention, and they just flopped," said Brad Adgate, an analyst at media buying firm Horizon Media Inc.

Each year, the networks spend hundreds of millions of dollars making and marketing shows, and advertisers drop billions of dollars buying commercials to run in them. If a show does not deliver the ratings a network promised advertisers, the network provides additional commercial inventory to the advertiser. For example, Fox's new singing talent show "The X Factor" delivered fewer viewers than advertisers expected, so the network provided what's known in the industry as make-goods.

Ratings are not the only factor in judging a show's performance. On paper, "Terra Nova" has been a solid performer for Fox, averaging almost 10 million viewers. However, the show — whose pilot alone cost $15 million to make — is far more expensive than the typical network drama. Given that, Fox was hoping it would deliver a bigger audience.

Neither "The Playboy Club" nor "Pan Am" were anywhere near as costly as "Terra Nova." However, NBC and ABC heavily promoted their respective shows — thinking they would connect with viewers — to no avail.

"All the buzz and hype really just works for the first episode," Adgate said. "This isn't like a movie where you have a great first weekend and make your money."

Despite some high-profile misses, overall it has been a decent season for the broadcast networks. The combined prime-time audience for the five broadcast networks — ABC, CBS, Fox, NBC and the CW — through the first 13 weeks of the season was 40.2 million, up slightly from last season. Given the increased competition broadcasters face from cable networks, which offer more original shows than ever, and new online platforms such as Netflix and Hulu, being relatively flat is considered a win for traditional media.

Among the bigger surprises of the season was the emergence of several new situation comedies that clicked with viewers. New hits include CBS' "Two Broke Girls," a raunchy comedy about two struggling waitresses; ABC's "Suburgatory," which is about a father and a daughter who struggle to adjust after moving to the suburbs; and "Once Upon a Time," a drama that puts a modern spin on classic fairy tales. Also breaking through is Fox's "New Girl" starring Zooey Deschanel as a quirky young woman trying to adjust to three male roommates. Even struggling NBC believes it has some building blocks in the romantic comedies "Whitney" and "Up All Night."

"This has been a year where comedy has shown great strength for every network," said Brent Poer, an executive vice president at advertising firm MediaVest USA.

Comedies are valuable to networks because they perform better in repeats and have greater long-term library value.

The biggest shock of the fall TV season was CBS' successful re-engineering of its top-rated comedy"Two and a Half Men." After star Charlie Sheen's highly public meltdown, which led to his being fired from the show this year, CBS gambled that "Two and a Half Men" could go on with a new leading man. And it looks as if the network's bet on bringing in Ashton Kutcher is paying off. "Two and a Half Men" is averaging almost 19 million viewers, a jump of about 25% from last season.

A case could have been made to just let "Two and a Half Men" end with Sheen's exit. If the reworking flopped, CBS would have been second-guessed for trying to carry on without Sheen instead of developing new shows.

For CBS and Warner Bros., which produces the comedy, it was crucial to show Sheen and the industry that one actor can't torpedo a hit.

"It was enormously important," said CBS Entertainment President Nina Tassler. "When a show is successful, it usually is never due to one particular element."

Thanks in large part to the re-energized "Two and a Half Men," CBS is in first place both in viewers and the 18-49 demographic coveted by advertisers. Besides "Two Broke Girls," crime dramas "Person of Interest" and "Unforgettable" have also exceeded expectations.

Despite the disappointment of "Terra Nova," Fox has something to celebrate. The network's prime-time audience jumped 17% to an average of almost 10 million viewers nightly. Even though "Terra Nova" and "The X Factor" did not deliver the kinds of numbers Fox wanted, they did better than what the network was airing in their time slots last season. "The X Factor" has already been renewed for a second season, but the decision to bring back "Terra Nova," which finished its 13-episode run last week, has yet to be made.

"This is a tough decision," acknowledged Preston Beckman, Fox's executive vice president of strategic program planning and research. "The ratings were good, not phenomenal."

Part of the problem for Fox is that "Terra Nova," which shoots in Australia, is not only costly but also takes a long time to produce. Fox needs to let the creative team behind the show know its fate before the network can assess the performances of new mid-season dramas "Alcatraz," "Touch" and "The Finder," which debut early next year.

The network with the most holes to fill remains NBC. Along with "The Playboy Club," other new shows failed to rejuvenate the network's lineup, including "Prime Suspect," a remake of the British detective show, and the romantic comedy "Free Agents." Overall, NBC's prime-time audience fell 10% this season to 7.3 million. Take out the network's NFL games on Sunday night and the drop is even worse — 13%.

"It was a tough fall for us," acknowledged NBC Entertainment President Jennifer Salke, who joined NBC less than six months ago from the TV studio 20th Century Fox Television. For the second half of the season, NBC has high hopes for "Smash," a drama about the making of a Broadway musical. Although Horizon's Adgate said it was a good show, he wonders whether it will appeal to a big audience. "Not everybody lives in New York or Los Angeles."

Salke argues that NBC's situation requires it to do anything but play it safe. "The shows have to … they have to be great."

joe.flint@latimes.com