The rest of the cast who weren't added DLC are pretty heavily sidelined, and in several cases, they basically vanish from the story. There is absolutely nothing wrong with a few hours of that, but it basically has to be what you're there for. It shows an alternate take on the last couple of chapters of the game, but it's mostly about Shang Tsung messing up everything. Overall, the story is kind of forgettable.
Pretty much all of the other characters serve minor roles at best, except perhaps Queen Sindel, who shows that her murder spree in Mortal Kombat 9 was no fluke. He's in almost every scene, and any scenes without him are significantly less interesting. Cary-Hiroyuki Tagawa's performance as Shang Tsung steals the show in every way, shape and form, and most of the story seems to be written to give him a chance to be various degrees of sarcastic, smug and snarky. The Aftermath story may as well be called The Shang Tsung Story.