Tammy is just okay, which translates into disappointing. I generally like Melissa McCarthy, but her shtick is getting old. I felt like I was watching the same (disappointing) character she played in Identify Thief, only this time she shares a car ride with Susan Sarandon instead of Jason Bateman. Or the same character she played in the more solid comedy The Heat with Sandra Bullock.
This time around McCarthy plays Tammy, an uncouth, disheveled-looking woman who totals her car, gets fired from her job at a fast-food joint, and walks in on her husband sharing a special moment with a neighbor. She looks for solace – and a car to borrow- at her parents’ house down the street. And next thing you know, she’s stuck driving her feisty alcoholic grandma (Sarandon) to Niagara Falls. If you’re hoping for a comedic version of Thelma and Louise, this aint it. 
McCarthy wrote the movie with her husband – actor and first-time director Ben Falcone. It has some funny, sweet, sad, and mildly-raunchy-but-entertaining moments, but it also takes a few wrong turns, particularly with the speedy and implausible evolution of Tammy’s character. I just didn’t buy it. I also couldn’t quite buy Sarandon as the gray-haired granny.
The movie has an impressive cast, but most of their talents are wasted in fleeting, undeveloped roles including Toni Colette as the neighbor involved with Tammy’s husband, Allison Janney and Dan Aykroyd as Tammy’s parents, and Sandra Oh as half of a lesbian couple with Kathy Bates. The performances are all decent, but most of the characters lacked any depth.
Tammy will make for an okay rental, download, or airplane time-killer, but there’s no need to rush out and see it in a theater. There are far better road-trip flicks to be found on the cinematic landscape.