Karma is almost a really good champion.
I have been playing her a lot and here are my thoughts:
Passive: I mean it's quite helpful, but it's kind of dull. Actually really dull. Very boring.
Q: This is so spammable I love it. It gives her enough damage in a many situations, but the AoE feels too small to effect team fights. The mantra is really good on Q. I love introducing myself to my lane opponent by taking a quarter of their health at least. Then in 1v1s it is really easy to rack up damage if you keep them in the manta Q area thing.
W: This is ok. I mean in 1v1 it's really easy to root the opponent. The damage is meh. The mantra on this is very situational. The only time I have found it to be game changing is when you are being dived and you don't have enough health and shield. In 1v1s it can win you the fight, but usually it is better to kill them quicker with mantra Q.
E: This is also spammable and I enjoy it a lot. Just this one ability taught me to use Alt+X to target myself with ease. I knew to do it before, but this helped me naturally do it. The mantra is really good on this godly IF YOUR TEAM USES IT. It's a goddamn shurelias with a shield. And it's on a super low cooldown.
R: I mean it's not a bad ability, but it doesn't do anything by itself so I have nothing to say about it.
Overall I really like her, but she is kind of dull.
P.S. 40% cdr is really fun on Karma.