If played at high levels, MK 1, 2 UMK3 and 4 are pretty solid fighters. UMK3 especially.MK ruined my love of fighting games and I stopped playing for years, sure it was fun and all until someone found the secret like fullscreen unblockable(you could dodge them I found out later), IKs .
Also MK is still a really bad game, there are plenty of better lol wtf holy **** broke *** games out there.
Only things really broken about UMK3 were Kabal, Human Smoke, Nightwolf and Ermac. Kabal's dizzydash could be done out of block and had a huge hitbox, meaning he could pressure you better than almost anyone. H. Smoke had a simple one-two pop-up combo that started out with a kick hitbox, so you couldn't duck to avoid it and could basically just crouch and block while he whittled away your life or timed you out. If he got the pop-up, you'd lose more than half your lifebar. Nightwolf was similar in that which his massive combo began with a kick hitbox, so he could endlessly pressure you. Ermac the same as H. Smoke.
Aside from that, it's a balanced, solid game. Played it online for years and I've only ever cursed those four characters. xP