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There's something about the Fockers.

Few sequels ever top their first chapters at the box office. But Ben Stiller's romantic comedy "Meet the Fockers" (search) managed to rake in a whopping $507.4 million worldwide after its release in December, besting the piddling $330.4 million its predecessor, "Meet the Parents," pulled down four years ago.

And it stands to make even more money when it's released on DVD next week.

But considering that the film was panned by critics and regarded by many viewers to be not nearly as funny as the original, how did this happen?

Richard Dorment, an editor at Giant, a men's entertainment magazine, said people will go see a second version of a movie if they loved the first one, no matter what critics say.

"It's like having a fantastic meal at a new restaurant: Of course you're going to go back. Except that on your second trip, your entree is cold and the waiter is rude," he said.

And even then they might return for one more course.

"You figure, 'Well, that must've been a fluke; I'll give it another shot.' So you return a third time and get food poisoning," Dorment added.

Traditionally, the sequel game has been a slow race to the bottom. For example, 1984's "Police Academy" grossed a then mind-boggling $81.2 million before taking a series of faceplants that ended a decade later, when the infamous seventh film in the franchise, "Police Academy: Mission to Moscow," (search) earned a mere $127,000.

But sequels can be a fickle business. Even two of the most famous follow-ups, "Superman II" and "The Godfather: Part 2," were panned by critics and had a lower box-office take than their originals. But the latter bagged six Oscars including best picture, best director and best adapted screenplay.

Stuff magazine Editor in Chief Mike Hammer noted that for every sequel success like "Hannibal" or "American Pie 2," there are long lines of duds like "Speed 2: Cruise Control," "Analyze That" and "City Slickers: The Legend of Curly's Gold."

But lately, a number of films have been breaking the mold. Aside from "Fockers," Dreamworks' computer-animated ogre-fest, "Shrek 2" (search) (which most critics said fell short of its former glory) nabbed the No. 1 spot for domestic gross last year, followed by "Spider-Man 2" in second place.

"Miss Congeniality 2: Armed and Fabulous" has pulled in a tidy $37.5 million domestically since it opened three weeks ago — and is well on its way to meeting the $106.8 million the first installment made.

The Sandra Bullock (search) vehicle is drawing viewers even though Roger Ebert called it "doubly unnecessary," ReelViews critic James Berardinelli likened it to "steaming sewage" and The New York Times compared it to "shoveling pig waste."

In fact, 18 of 2004's top 100 domestic-grossing films were sequels, with five making the top 10 and a total gross of $2.33 billion. In 2000, only nine of the top 100 grossers were sequels, only one cracked the top 10 and their total take was $711.8 million.

So what separates the sequels that bomb from the sequels that fill up theaters?

Often, it's more about the characters than the actors.

"In the '80s, [Sylvester] Stallone could have had Rocky have a sex change operation and it would have drawn at the box office. But that was more about Rocky than Stallone," Hammer said. "'Stop, or My Mom Will Shoot' was a good indication that movie fans would rather be beaten to death by Rockys than watch Sly try to be Ben Stiller."

In other cases, however, it's all about star power.

"I'll see basically anything with Sandra Bullock in it. I like her style, her flair," said one woman at a recent screening of "Miss Congeniality 2" in New York City.

Indeed, a movie like "Fockers" has cross-generational appeal with Stiller, who appeals to a younger crowd, and Robert De Niro, Barbra Streisand and Dustin Hoffman for the older folks, not to mention a plot that focuses on the universal plight of dealing with in-laws.

But Kim R. Holston, author of "Science Fiction, Fantasy and Horror Film Sequels, Series and Remakes," said successful sequels like "Meet the Fockers" also pay attention to character and plot continuity.

In other words, just remaking the same movie in a new location and slapping a Roman numeral on the end is a recipe for disaster.

"If you don't care about the movie itself, you are going to prostitute it, you're going to screw it up somehow," he said.

Holston points to flops like the "Predator" and the "Friday the 13th" sequels that didn't make sense to fans who were actually interested in the story itself.

Meanwhile, the most successful "Friday the 13th" sequel, 2003's "Freddy vs. Jason," included a scene in which the characters self-consciously detailed the absurdity of the franchise's arcane 11-film plotline.

Dorment thinks the success of "Meet the Fockers" might be enough to draw viewers back for one more helping.

But if a franchise repeatedly lets down its fans, it's unlikely they'll return for another episode.

"I give it one more before Stiller needs to watch his back," he said. "After that it'll be 'Meet Your Maker' for Ben."