What is fun about Katarina?

Everything. The "challange" of getting a FULL ult off. The trill of the resets. the PJ Salt i get when i get camped. Everything. I think shes fun as hell and that is all that i care for.

Very smooth kit, her abilities flow together perfectly.

Part of it is seeing the rage from the enemy team when they can't properly CC you.

Her abilities all complement each other. Even Yasuo has that tacked-on windwall that doesn't really synergize with his other abilities, with Kat there are no questionable things in her kit. She is good at killing and nothing else.

Her combat pattern occurs at lightspeed (which is one of her issues) but she makes it look great. Also, she's the only assassin who WANTS to teamfight, so she's unique in that respect.

my fav assassin but 100% ban rate in my elo

Solo carrying to Diamond. That's what's fun.

How great her kit works, the ability to outplay with resets, getting flamed for getting full ults off in teamfights because the enemy team doesn't know how to CC. Fun to make junglers look silly with ward hops. Everything about her is fun.

The fact that she either does VERY VERY good.... or VERY VERY bad.

The baron and dragon steal's aren't bad either ☺

This is a while after you uploaded this post, but as an aspiring kat main I wanted to share my knowledge. Katarina is fun because she is so difficult to play, but so rewarding when you do it. Getting multikills feels so amazing, and it looks amazing. The thrill of dancing between the enemies while killing them is fabulous.

Combos are smooth, the thrill of not ever getting CC'd and button mashing is pretty fun. Also I like killing things really fast and she's the only assassin who wants to teamfight.