I love True Detective. I love the eerie, deserted bayou setting, Woody Harrelson and Matthew McConaughey playing against type as well as playing off each other, and the themes of existential horror as personified by that hulking figure in the tighty whities and the gas mask.
Imagine though, if any of the actresses had the opportunity to play characters as complicated as Martin Hart or Rustin Cohle. Imagine especially what Michelle Monaghan could have done with a character who did more than nag her husband or seek out revenge sex against him, or who had more scenes on her own that would give more insight into her own motivations and the personality behind them, instead of falling back on the notion of "that's what scorned wives do" or even "this is what would hurt this specific husband the most."
Imagine if she had better roles to play in general. Because Michelle Monaghan has been in several interesting movies, and the common thread between her characters in them is that they're mostly silent, underwritten observers of the boyfriend/husband/male love interest who is the actual star. This is true in Mission Impossible III and in Source Code, where she's the damsel in distress that Tom Cruise and Jake Gyllenhaal want to save, respectively. She plays the female lead in Eagle Eye, where her character is forced by an evil computer to carry out an attack on the government (or is the government evil?). However, her fellow manipulatee, played by Shia LaBeouf, gets more agency and a more interesting back story involving a difficult relationship with the rest of his family and feelings of failure, while she is pretty much the cliché of a mother motivated by protecting her son.
Her characters do get a showcase, though. In Eagle Eye it was a scene or two in which she feared that she was a bad mother, and in Gone Baby Gone, the movie built to her perspective in the missing children's case that she and her boyfriend/partner Casey Affleck were solving. Gone Baby Gone has stuck with me because after seeing it with some college friends we argued heatedly about whether Ben Affleck underwrote Monaghan's character, who gets one line of backstory from another character, about her being stuck up, and who usually says no more than two lines in the film's various interrogation scenes.
Upon rewatch, her silence in the movie makes sense. Gone Baby Gone is clearly set in a man's world, as exemplified by a scene where she and Affleck question a witness in a Boston townie bar, and then another patron threatens them both with the line, "Cause there's some fine pussy in this place tonight." With risks like that, what room does a female private investigator have to go on the offensive? The contrast between her style and Affleck's also has its use. While Affleck gets to connect through dialogue with the supporting characters and thus show how he's ultimately of South Boston, her silence allows her to observe as the "stuck up" outsider, and thus come to a different conclusion. Monaghan does a lot with her reaction shots in this movie.
She also does a lot with actual lines. This is clear in her 2005 breakout role in Kiss Kiss Bang Bang, where on the one hand she plays Robert Downey Jr.'s love interest (not to mention the object of his white knight complex), but on the other hand, gets to talkatively drive the mystery in that film. The nutty investigation that the movie is centered around has everything to do with the tragic past that her character came from, and the writing portrays her as the smartest person in the room, the one who brings in the leads whereas the male characters are content to let the evidence gathering stall.
However, Kiss Kiss Bang Bang still unfolds mainly from the point of view of men who are deeply insecure about how sexual a woman can be. That means she has to face the indignity of Downey's character bitterly reminiscing about how she fucked every guy in their hometown except for him with little room to defend herself. To bring it back to True Detective, playing a female supporting character means existing to reflect Marty and Rust back at themselves. Shen only changes to veer very closely to the "crazy bitch" stereotype, where her getting revenge on her husband is her main concern. Honestly, the only way those pivotal but upsetting scenes with Rust and then Marty were the least bit palatable were because Monaghan's performance elevated them. Her facial expressions in the "afterglow" of the former scene in particular adds some ambiguity to how what happened affects her character emotionally, as well as giving some hint as to what internal life led her to the decisions she makes.
It's no coincidence that Maggie Hart's showcase episode was True Detective's most boring episode yet, or that in the penultimate episode, she's just there to come to a reconciliation of sorts for Marty and Rust that involves nothing more than expressing concern for them. When the female characters have done randomly upsetting things before, the show has balanced that with other instances of fascinatingly staged menace and violence.
One can argue though that in a limited amount of time, none of these projects that I've mentioned have the space to accommodate more back story and dialogue from Monaghan's characters. This is why she needs more lead roles, besides the roles in indies that most have never heard of. This is why there should be more projects about women, instead of supported by women. Otherwise, you get an actress like Monaghan who has to elevate a thinly sketched character in movie after movie, who has to glide through projects concerned mainly with masculinity as the girlfriend, wife, or mother without making too many waves.
That's not to say that how she does that isn't impressive. It's just that she deserves better. True Detective Season 2, anyone?