Her kit flowed really well in avery good way. Its like Lee Sin's kit without being overloaded. It allowed you to confront several situations with different abilities not always in the same ''rotation''.
Her passive was a less hp more ap passive that could have been gone or reworked. It was pretty much a non issue if it was deleted.
Her main feature was Mantra, her Ult, that unlike the new mantra added effects to her spells that complemented her theme. Her defensive spells gained an offensive edge and offensive spells gained a defensive edge. It also had 2 charges and less cooldown. Her abilities had 6 levels too since mantra was a one point wonder (like actual Jayce/Elise).
Her Q was a conical damage spell similar to Morde's E. Mantraed it became an AoE heal that healed for a base plus a % of missing HP, on top of the damage with was pretty good.
Her W was a tether that had various effects, mainly on the target. If allied it speeded them up, if an enemy it slowed them down. Whatever was the target, allied units that touched the tether itself were speed up by it, and enemy units were dealt damage. Mantraed it doubled it haste/slow numbers. It started underwhelming earlygame, but at level 6 it was ridiculus at 40% cdr: it had a 5s duration on a 6s cd. It had a 85~% uptime for a constant 20% haste for your entire team or a permaslow, 40% if mantra'ed.
Her coolest spell was her E, which was a single target shield with the biggest ratio and base in the game back then. Kinda like Janna's but the difference is that Karma's was much better with AP, so her shield quickly outscaled Janna's. Mantraed it dealt damage around the shielded unit equal to the shield's numbers. it was an awesome ability that allowed her to stop bursty all-in and counter assassin midlaners that werent LB.
Her weaknesses where pretty clear too: Low range, no mobility, mana hungry, no hard CC. Lux was her worst match up back then, a good Lux could keep Karma at bay and poke her out of mana and out of lane. One of her best match ups was against Diana because the moment Diana tried to all-in Karma she was met with a shield and respectable burst plus a slow.
sigh I miss Old Karma.