Tried her a few times on PBE and I'm impressed. I'm not a big fan of exactly how her kit was done (I wish her elements had a bigger change on her passive), but I felt really happy that she wasn't terribly weak nor was she actually too strong. Since Qiyana lacks many of the mechanics that made previous champions way too powerful (healing, shields, un-targetability, long range spells, point and click spells, etc), she honestly feels really satisfying to play.
QIyana does a lot of damage but unlike many champions, she can't just face tank and deal her damage since she has nothing to protect her without sacrificing her build. Not having the healing, shields, etc. really makes such a huge difference and I feel so happy that she doesn't have any defensive utility outside of her Bush element stealth. She's a champion that you actually need some skill to play, and she has a really high skill ceiling with all the mobility provided.
Nearly every champion, as far back as even Azir, I've felt like their kits just had way too much safety cushion. Champions like Jhin who have massive range ult, root, slow traps and speed boost... then Illaoi and Kayn with their massive healing.. Basically every recent (or semi-recent) champion has just had no risk involved with how they deal their damage, and this is the first time in so long that I finally don't have that feeling after trying the champion out.
I tip my hat off to you employees at Riot Games, great job.