Kalista 37.5% Win Rate
Kalista has a win rate of 37.5% as of 11/21/2014. This is her first day of release. The games taken included all games ranked Diamond V through Challenger, only. There were 472 games played that included Kalista. Out of the 472 games, Kalista was on the winning team for 177 and on the losing team 295 times.
( 177 / 472 ) = 37.5%
These included the games from the following regions:
North America Europe West Europe Nordic & East Brazil Turkey Russia Latin America North Latin America South Oceania
Keep in mind that players will learn to counter her and play her better over time!
Edit: It is still very early in her release and by no means a good measure in her power level. Even since the time of posting the statistic changes to 36.3 from just 50 more games and will continue to fluctuate.
However, In the arguments regarding how she is doing so far, there is a much discussion of opinion and very little facts. Most of the experiences have come from just a few games. The larger the sample size, the greater the accuracy. Thus, though very little to work with, this is all we have at the moment.
Raw information provided for you to be the judge--even if only to dismiss it.
Day 2 Update: ( 1158 / 3296 ) = 35.1% win rate Day 3 Update: ( 2232 / 6141 ) = 36.3% win rate Day 4 Update: ( 2565 / 6953 ) = 36.9% win rate Day 5 Update: ( 2922 / 7806) = 37.4% win rate