Look. George R.R. Martin's A Song of Ice and Fire series is roughly 3.7 times longer than the Lord of the Rings trilogy, and we're only up to book five. If you're trying to cram that monstrosity into a TV show, things are going to have to be cut. Entire story-lines and countries and plot-points are going to have to be cut. That's the nature of adaptation. I accept that. But I am forever mad that we lost the single most bad ass, vengeful zombie mom in the whole of Western Literature. Lady Stoneheart shouldn't have been cut from "Game of Thrones," because she's more than just another undead monster to defeat. Martin himself fought to keep her in the show, but Catelyn Stark's fate wasn't deemed important enough for the HBO audience. Spoilers ahead!
In the books, see, Catelyn Stark dies at the Red Wedding, much like her television counterpart. In both versions, her body is thrown into the river as a cruel joke about her family sigil being a fish. In the show, we quickly move on to the next several dozen subplots, and Catelyn is all but entirely forgotten, even by her children (although to be fair, they have enough problems of their own).
In Martin's story, though, a lot more time is given to the Stark kids missing their mom. Young Arya, especially, has nightmares of trying to reach her mother across a vast, confusing landscape. She also has dreams that she's seeing through the eyes of her wolf, Nymeria.
As Nymeria, wandering through the woods one night, she comes across a familiar corpse and drags Catelyn's body from the river. She runs off when humans approach, and Catelyn is found by Beric Dondarrion. The resurrected outlaw gives his life for hers in a Red Priest ritual.
The next time we see Catelyn, she has been reborn as the Lady Stoneheart: a living corpse with a slashed throat, who has taken command of the Brotherhood without Banners. She's determined to seek out and kill every last Frey, Bolton, and Lannister, as vengeance for her murdered family:
She don't speak. You bloody bastards cut her throat too deep for that. But she remembers.
In the show... Catelyn stays dead, and the entirely pointless character of Beric Dondarrion (the eye-patch guy) putters about for another couple of seasons and journeys north with Jon Snow and the gang on their all-male zombie-catching road trip in season seven.
The HBO adaptation is, apparently, fine with undead characters. Jon is undead. Beric is undead. All those wights they're fighting in the snow are very, very undead. But an undead mom would be pushing it too far. Dead women in TV shows exist primarily to give motivation to men around them, and maternal figures aren't supposed to come roaring back from the grave as subversive outlaw zombie queens, so Catelyn stays firmly deceased.
It seems strange that the undead lady outlaw is cut from the show, and replaced with an undead dude outlaw who becomes one of our protagonists.
But then again, how are TV viewers supposed to empathize with a woman who is both hateful and ugly?:
...her face was even worse than he remembered. The flesh had gone pudding soft in the water and turned the color of curdled milk. Half her hair was gone and the rest had turned as white and brittle as a crone’s. Beneath her ravaged scalp, her face was shredded skin and black blood where she had raked herself with her nails. But her eyes were the most terrible thing. Her eyes saw him, and they hated.
And yet somehow, despite all this, we can empathize with Lady Stoneheart in the books. She's an antagonist for sure. But her violent hate comes from her anguish. She didn't want any part in the politics of Westeros, she didn't even really want to marry Ned Stark back in the day, but she came to love Ned and her children. And now (as far as she knows) they're all dead.
Also, the Red Wedding was a very uncool move, and she wants the world to know.
Beyond the iffy gender politics of cutting Lady Stoneheart in favor of more quality time with Beric "Who Cares" Dondarrion, the TV show completely misses the point of having Lady Stoneheart in the books at all.
She's not just another minor villain to pass the time before we meet the big boss snow zombie. She's there to complicate the morality of Westeros.
At this point in the plot of the TV show, the White Walkers are pretty unambiguously evil. They're stomping around killing people and sticking blue contact lenses on babies.
In the books, though, we know very little about the White Walkers. We know they're bringing their zombie army southwards, and we know that they're dangerous, and somehow magical. But we don't know why they're doing this. We don't know what they want. They, like Lady Stoneheart, might even be seeking justice. Just because they look completely Other doesn't mean that they're senselessly evil. Martin has already promised us that the series isn't going to end in an epic battle of good vs evil — his stories are always more complicated than that.
Lady Stoneheart also forces us to reckon with the overwhelming cost of war. Last we saw her in the books, she was about to kill Brienne of Tarth for breaking her word and working for the Lannisters. Clearly, as readers, we're on Brienne's side, since Brienne is our buddy and not a rage-consumed zombie. But Brienne is all about keeping her oaths, and Stoneheart is here to remind us that our most honest character has become a hypocrite in order to survive.
More than anything, though, Lady Stoneheart is a voiceless advocate for the voiceless. Beric gives his life for hers because she can lead the Brotherhood without Banners better than he can: their group's only purpose is to advocate for Westeros. For the innocents who've lost their lives while noblemen fight over a metal chair. Catelyn never wanted to get dragged into the political intrigue and the fight for the throne, but she lost her husband and children to it all the same.
She's literally a dead woman come back to life, but she's also a stand-in for all the "defenseless" characters who are killed by the more powerful. Even if she's overdoing it a bit on the whole revenge-and-murder thing (and she definitely is), she's a powerful reminder that you can't have high concept battles for ideals without very real casualties.
So yes, it would have been cool to see Michelle Fairley all done up as a vengeful zombie. But more than that, it would have nice if the Game of Thrones adaptation remembered that there's more to this story than the actual throne.