Yeah, right off the bat, Noob and Rain are broken. The bosses are Broken.
Once they are taken away, the game is still unbalanced, but those characters shatter the planet.
MK2 Kung Lao is pretty broken as well. He does MK2 level damage, is extremely fast, and has a very simple, big damage combo. Baraka can do massive damage in a few simple hits too. And he also does MK2 level damage.
MK2 Kung Lao, MK2 Jax, Johnny Cage, and Baraka do MK2 level damage. MK2 Raiden does MK3 level damage and he seems like a pretty decently balanced character.
Kung Lao's spin disables, which is a balancing effort, but then it can move, which just breaks him in a different way, lol.
And then if you are talking about N64, there are a lot of problems with the gameplay overall that break it in addition to the add-ons that break it.