The bathroom jokes and phallic humor start early in "Vacation," as the opening credits roll against a backdrop of typical tourist photos marred by unfortunate accidents. That sets the tone for this raunchy but toothless follow-up to "National Lampoon's Vacation," the 1983 comedy classic about a pleasant family road trip that spirals into insanity and death.

Therein lies the difference between the two movies. The original, directed by Harold Ramis and written by John Hughes (from his short story "Vacation '58"), cast Chevy Chase as Clark Griswold, a Midwestern patriarch determined to drive his family to a fictional Los Angeles theme park, Walley World. What followed wasn't just a comedy of errors but a merciless savaging of the American family ideal; even elderly aunts and small dogs weren't safe from the movie's wicked humor. Long before "Little Miss Sunshine" (2006), there was "National Lampoon's Vacation."

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In the new version, Clark's son, Rusty, has grown into a good-hearted doofus (Ed Helms, to the manner born). Rusty has a supportive wife, Debbie (Christina Applegate), and two kids, snotty Kevin (Steele Stebbins) and sensitive James (a very good Skyler Gisondo). For some reason, Rusty remembers his old Walley World journey fondly and decides his own family should experience it.

That they do, re-enacting and slightly tweaking the first film's more memorable moments: a robbery, a Grand Canyon misadventure, a quick visit with kooky family members. (Leslie Mann plays Rusty's sister, Audrey, while a game-for-anything Chris Hemsworth plays her cocky husband. Chase, as grandpa Griswold, also appears.) Many of the movie's jokes fall into the "oops" category, as in: Gee, this natural hot spring smells a lot like sewage. And so on.

The original "Vacation" wasn't exactly highbrow, either, so why does this one pale in comparison? Partly it's the script and directing, both a little choppy, by Jonathan Goldstein and John Francis Daley. Mostly, though, it's that American families are no longer the unassailable, sacrosanct ideals they used to be, so putting one through the wringer isn't funny in and of itself. The new "Vacation" scores a laugh here and there, but it also proves the adage that you can't go home again.

CORRECTION: An earlier version of this review misidentified the relationship between Audrey and Clark.