I just recently picked up Karma, and let me tell you something, she's stronger than most ap mages, and provides immense utility with high burst damage.
Note that this is not a "Nerf pls" thread, as I do enjoy playing Karma, and while being "too strong" I don't think she's overpowered.
You can play her literally anywhere, Top, Jungle, Mid, Support even AD Karma is strong due to her aa range. But why I think she's too strong? Because of her ultimate, her Q base damage with ultimate is 540 + 120 explosion damage at maxed rank. And her spammable shield that gives movement speed turns you into a train with 40/45% cdr. You can basically always use it to travel the map without losing too much mana. With a chalice ofcourse.. Her W, a damaging snare, is also quite spammable, making running away from her not an option if you don't have flash available..
But yeah, even though she's quite strong, she's still paper without any defensive items. I guess that's her balance
ALso I don't get it why is she so underplayed.. So sad :/