The Big Wedding is a big mess. First clue: all-star cast. Second clue: gratuitous f-bombs and a few seconds of nudity designed to clinch an R rating. Third clue: a contract required by Lionsgate, insuring that I will reveal nothing about the movie before 9:00 p.m. CDT on April 25 and will share no spoilers ever.

There are some laughs, to be sure, in The Big Wedding, though not as many as one might hope for. The set-up: Robert DeNiro and Diane Keaton are exes. Susan Sarandon is DeNiro’s girlfriend. Adopted son is about to get married. Son’s bio-mom from Colombia is strict Catholic who doesn’t believe in divorce, so son asks DeNiro and Keaton to pretend they’re still wed while bio-mom is visiting. Hey, successful film and TV comedies have been built around flimsier situations.

The bride (Amanda Seyfried), her parents, other extended family and even the priest (Robin Williams) provide additional sub-set-ups. In most cases, you can figure out exactly what’s going to happen.

Apparently Topher Grace is now out of the witness protection program or rehab or wherever he’s been. He plays DeNiro/Keaton’s son who receives a dinner table sexual favor in a scene that was much funnier eight years ago in Wedding Crashers. Katherine Heigl, whose ’09 movie The Ugly Truth similarly ramped up the raunch, rendering an R-rated romcom, plays Topher’s sad sister.

The Big Wedding provides a modest amount of amusement. It runs just 90 minutes which means, with 20 minutes of trailers beforehand, you’ll barely have time to finish that mondo-size box of Raisinets.

The cumulative star power of a movie like The Big Wedding (and various Garry Marshall holiday-related films) actually can, I believe, make such a movie more bearable. On the other hand, if you go because you particularly like one individual star in the cast, you will inevitably be disappointed because your favorite has to share his or her screen time with so many others.

And maybe the R rated content will please many who tire of formulaic PG-13 romantic comedy fare that toes the line. In a world with HBO and Showtime original content dialing up the sex/language quotient, The Big Wedding could be right on the money with its f-bombs and bare butt. But I don’t think so.

(Special note to the Lionsgate legal team vetting this review for spoilers: I’m flattered that you care! Reminder: If you were required to watch this mess, that’s 1.5 billable hours!)