As a Karma player I have to say she is effective enough, possibly even viable, but outshone by other champs. She does a nice mixture or damage and support and does it very quickly so it is difficult to stop her contribution to a team fight. Unlike some people comparing the damage to an ultimate it recharges MUCH faster. Under 30 seconds faster.
As much nice stuff as she has though she does not fit in the current meta and can be countered IF YOU KNOW HER. Range and harrass by a smart player can cripple a karma. Even if it doesn't force her out or zone her it keeps her mantra and mana reserves low, leaving her prime for a gank, especially since she is very squishy without shield and only moderately durable with it. As well early game you are forced to choose between damage and your only lackluster form of CC, spirit bond. Spirit bond has it's uses but until later game is mostly a waste and the spell badly needs some added utility or viability added to it. Expecting to deal damage with spirit bond in a team fight is unreasonable and when clearing monsters and creeps it's unneeded.
She can dominate normals like no tomorrow. Very few people know how to deal with her and her fulcrum shift nature punishes lack of awareness and not taking her presence into account pretty obscenely. 3 vs 1 ganks can easily turn into a 2 vs 3 win with the arrival of a Karma. Karma also excels at pushing lane, an unwanted addition early game but mid game and on she can nearly walk straight up a lane and kill minions only by pausing briefly. She can then shield individual minions from turret fire and heal the entire wave of them. This is another strength that can let her easily dominate normal games.
Unfortunate fact of the matter is that experienced players can mitigate her impact greatly however. While this won't make her worthless by any means, it makes many other champions hands down better picks in high skill game play. Part of this is the meta, part of this is her low range and ability to be countered with top notch game play.
In an attempt to help give her a bit more utility I came up with a change to her spirit bond noted here (plus buff her horrible AA range):