It was bound to happen. Disney's (NYSE: DIS) Pixar couldn't crank out critically acclaimed movies forever.

This weekend's release of Cars 2 is Pixar's first theatrical release to be widely panned by film reviewers. As of this morning, just a third of the 147 vetted critics tracked by Rotten Tomatoes liked the computer-rendered flick.

It's not just the natural bias against sequels. Cars 2's embarrassing score of 33 (or a 33% freshness rating) is in sharp contrast to the stellar scores of 100 and 99 that Toy Story's follow-ups received. Even DreamWorks Animation's (Nasdaq: DWA) Shrek the Third -- the third and most critically dissed installment in the rival studio's biggest franchise -- managed to woo 41% of its jaded critics.

Disney shareholders will argue that professional reviewers are irrelevant. Families are the ones that will ultimately vote with their pocketbooks, and Cars 2 was a hit over the weekend. The sequel -- that moves Lightning McQueen and his loyal sidekick Tow Mater overseas -- sold a whopping $68 million in tickets through 4,115 North American multiplex screens.

For those scoring at home, that is three times more than the box office receipts generated by Disney's celluloid dud Mars Needs Moms earlier this year. It was that film's disastrous showing that forced the media giant into a rare quarterly miss. You won't be seeing Mars Needs More Moms anytime soon.

However, let's not dismiss the low Rotten Tomatoes -- or rotten Tow Mater -- scores so quickly. Of course Cars 2 was going to have a blowout opening. The original release reportedly spurred nearly $10 billion in global merchandise sales. Ticket sales will fall off quickly if negative word of mouth begins making the rounds. Given the merchandising juggernaut of the franchise, a sharp drop off in interest will hurt Disney far more than even Mars Needs Moms' fiasco.

Then again, there probably aren't too many boys under the age of 10 in Rotten Tomatoes' pool of pro critics. It's the youngsters that will decide if the film is a winner or a loser, though parents may think twice about giving it a repeat screening or paying a premium for one of the IMAX (NYSE: IMAX) showings if it's not entertaining to them.

This has certainly been a strange year in animation. Rio and Rango -- put out by News Corp.'s (NYSE: NWS) Fox and Viacom's (NYSE: VIA) Paramount, respectively -- were springtime hits. Disney flopped with Mars Needs Moms, and shares of 3-D outfitter RealD (NYSE: RLD) took a hit last month after DreamWorks Animation's Kung Fu Panda 2 disappointed investors by grossing less than the original.

There are no more certainties in theatrical animation. You don't need to be a big name to have a hit. You can't assume that a killer franchise will be sustainable. In the eyes of critics, at least, Pixar is no longer perfect.

Did you catch Cars 2 over the weekend? What did you think? Share your thoughts in the comment box below.

Motley Fool newsletter services have recommended buying shares of Walt Disney, DreamWorks Animation SKG, and IMAX. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.

Longtime Fool contributor Rick Munarriz can usually be found at Walt Disney World. Not today, though. He does own shares in Disney. He is also part of the Rule Breakers newsletter research team, seeking out tomorrow's ultimate growth stocks a day early. The Fool has a disclosure policy.