Cobb's wife. She could be a great femme fatale nemesis, but instead, we get a passive aggressive memory who keeps making a nuisance of herself. She doesn’t do anything, she’s not interesting, she adds nothing. She could have been part of the team at the beginning of the movie, that would allow me to actually care about her being dead.
The current Mal could still be effective, if she was haunting Cobb. Two things ruin this, however. First, she does more harm to Cobb’s friends- she shoots Arthur in the leg and insults his taste in expressionist art (that bitch!), she lunges at Ariadne, she shoots Fischer. She barely harms Cobb at all. Now, if whenever Cobb was isolated in the dreams, she appeared and relentlessly closed in on him with ruin in her wake like some pyramid head without the pyramid, it would be a whole different story. Second, Mal is awfully needy. Every time she shows up, she does nothing but yell “me me me why is this dream not ALL ABOUT ME!” It’s obscene and irritating. So many times I wished Cobb would glare at her and yell “Mal, can’t you see I’m busy here? Just bugger off now will you, I don’t have time for your bullshit right now!” Whenever she shows up, Cobb almost instinctively begins to defend against her- he doesn’t seem particularly entranced by memories of his love either. It’s not that he wants her in his mind but knows surrendering to that memory will destroy him. He doesn’t want her there at all, and she is too obnoxious to leave.