Ever since her breakout performance in "Bridesmaids," in which she played the lovable but tough Megan, Melissa McCarthy has been saddled with roles that fail to capitalize on what made people love her.

Gone is the endearing persona, and in its place are unlikable characters in a series of disappointments like "Identity Thief," "The Heat" and now, perhaps the biggest disappointment of them all, "Tammy."

McCarthy plays Tammy, a woman having a bad day in the midst of a bad life. She loses her job, her car breaks down on the way home and, when she finally gets there, she finds her husband (Nat Faxon) cheating on her with the neighbor (Toni Collette). It's off to her mother's house (a couple of doors down the road) with a declaration that she's taking a road trip. Mom (Allison Janney) won't let her borrow her car, but Tammy's boozing grandmother Pearl (Susan Sarandon, fully immersed in the role, down to the high-waisted pants) is up for the trip, despite some serious medical conditions.

The road trip, destination Niagara Falls, is a disaster, with lots of drinking, a robbery, promiscuous behavior and even some explosions.

The acting isn't the problem here -- McCarthy and Sarandon play their parts well. The problem is that "Tammy" is the kind of film that spirals down further and further with these unlikable characters, until you hit the last few minutes of movie, when you're supposed to feel for them in the final redemption scene. By the end of "Tammy," you've been burned for so long that you just don't care anymore, as long as it's ending.

Kathy Bates steals the show here -- which isn't particularly difficult to do -- as Lenore, Pearl's tough but lovable cousin with a penchant for blowing things up. Dan Aykroyd, for the trifle of minutes he's on screen, is as funny as he's ever been. Can somebody please give these two some good roles?

The rest of the admittedly impressive supporting cast isn't given much to do. Collette barely has any lines. Lenore's partner Susanne, played by Sandra Oh, is just kind of there. Gary Cole and Mark Duplass, who play father and son, are fine but unmemorable. At least Cole -- playing a hard-drinking ladies man -- looks like he's having fun here. At least somebody is.