League of Legends (LoL) Question: How good is katarina

As in all cases, it depends. Kat is a burst assassin, so her kit is entirely based off mobility and damage, not survivability. She is an amazing champion if she can snowball, but she has hard counters and can be punished for being out of position. Her usefulness also depends on the person you are in lane with and the composition of both your team and the enemy team. I know that's not helpful, but that's the best answer you can get.