Melissa McCarthy's "Tammy" kicked off its Independence Day weekend release with a solid $1.3 million at the Tuesday night box office, but critics are saying McCarthy and husband Ben Falcone's dream project is just not that funny.

McCarthy plays the title role in "Tammy," the story of a fired fast food employee who takes a road trip with her alcoholic and promiscuous grandmother (Susan Sarandon). Toni Collette and Kathy Bates also star.

Reviews so far have not been so kind, with the film earning only a 21% approval rate on Rotten Tomatoes.

Variety's Justin Chang called the movie a "middling misfire" which "never rises above the level of amiable mediocrity." But critics' assessments of the raunchy comedy go south from there.

USA Today says, "Tammy aspires to be a latter-day 'Thelma & Louise,' and since it co-stars Susan Sarandon, one could say at least it has its Louise. But that's about it."

Time's Richard Corliss snarked that "Tammy" "could be an artifact from some alternate universe: the creatures there resemble Earthlings but have an entirely different and debased idea of what's funny. Arriving in time for the July 4 weekend, 'Tammy' has the effect of a shoddily manufactured firecracker that weakly goes off in your hands -- leaving no permanent damage, just a bitter memory."

Some of the reviews were pretty harsh, with the Hollywood Reporter saying, "The film progresses from merely unfunny to unconvincing to dull." The Seattle Times agrees: "It just isn't very funny."

Christy Lemire, writing on RogerEbert.com, was somewhat kinder, though she agreed with most reviewers that McCarthy's shtick is starting to wear thin. But "the intention is admirable," she wrote, "as is the focus on flawed female characters and the way they relate to each other."

Still how dependent on reviews is the box office success of the film? "Tammy" is up against two other movies with less-than-favorable reviews this weekend--"Transformers: Age of Extinction" and "Deliver Us From Evil."

Even with the critics' disapproval, McCarthy's star power may be enough to get people into the theaters.

"Tammy" is expected to earn $40 million over its first five days of release.

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