I listed the following:
1) Kitana killed off Shao Khan. In a narrative perspective, it made sense since this was long overdue for her development because of what Shao Khan had done to her family and Edenia after finding out the truth since her debut in II. It also coincided with the second point...
2) Kotal Khan handed over his title as Khan to Kitana. Many fans were mad about the way the story handled him: he couldn't overpower Shao Khan twice, his second fight made him crippled before Kitana intervened. Not to mention, he was about to exterminate the Tarkartans before Jade chewed him out (still surprised Jade even hada lover and its him).
3) D'Vorah on a mad killing spree, she even killed off Kitana's real father, Jerrod. Fans were pissed at her for killing off the present Scorpion, aka Hazashi.
4) Dark Raiden suddenly disappeared when the past selves of the good guys came along.
5) Something about the non-canon ending of Jax. Discussion went political... I'm going to have to play him to see this.
6) Most of the new characters: Centrion and Geras, especially did not do much.
7) Frost was hyped from everyone but she didn't even do as much, just being a brat and annoying.
And what I'm hearing that the fans want the bad guys to win but they were low-key winning in previous games. 9 especially because the majority of the heroes like Jax, Kung Lao, and Kitana were killed off by Sindel powered up. Raiden, Johnny and Sonya were the only ones survived so it was heavily bittersweet. And Quan-Chi was the key winner because he had majority of the heroes as Revenants for Shinnok. Same thing with 10, though fans were mad that Cassie killed Shinnok.