1) no originality or anything special in all characters after mk3. no character in mk4 and onwards has real personality or anything too special to offer except for Reiko & Frost imo
2) Stryker, Meat, Mokap, Bo' Rai Cho, Drahmin, Hsu Hao, Chameleon, Khameleon, Motaro in MKA, Reptile without human form. those are just disgusting.
3) Noob Saibot's name.
4) palette swaps and lack of originality in kickass characters with tons of potential
5) not having a solid story from the start for the first-ever characters and then finding a way to glue the new characters in. too many story changes or blanks that make it look cheesy.
6) babalities/friendships/animalities
7) cyborg Smoke. and by that, I mean that I'd want the character as he is entirely but NOT as human Smoke turning into him and having to wonder each time if Smoke will be human or a cyborg in the game. I'd want smoke without the smoke coming out of his body but all the other moves to stick (different name too, obviously). on that topic, human Smoke with his own moveset ffs
8) many many MANY more special moves, like subzero's iceball, scorpion's spear, stuff like that. imagine a mortal kombat game with like 1656165 simple or special moves per character

9) ability via the options for one button fatalities, some are just too hard to pull off and it's irritating
10) 3D