The effort in 4.21 is commendable, but despite these efforts, Cassiopeia is still not what she needs to be thematically and in game play.
First of all, while the tweaked passive does technically kick in faster, again, this is an element I do not like nor do many other players of Cassiopeia. Her strength is still locked out until milestones, now governed by time more than anything. In the matches I've played with the new numbers, it still takes more time than necessary to get her to where she needs to be to not be dead weight against champions who can quickly overwhelm her while she is still struggling to bring herself to their level. Regardless of whether or not she's "OP" and an end game melter of faces, this is not the direction that Cassiopeia should have been pushed into.
Secondly, the overloading of E is becoming an issue. I'm sure you've heard the KISS acronym before. Keep It Simple, Stashu. E at the moment is excessively overloaded and does entirely too much. As many have mentioned before, we don't like an E centric Cassiopeia kit with her poisons as an afterthought. An amp on E is appreciated, but it doesn't get back to the problems she has - she is a flimsy mage with pitiful range with E, and forcing her into close proximity against almost any other mid retards her effectiveness. With her posions only lasting 2-3 seconds unless the opponent is camping in a Miasma, this amp is ineffective at giving power back to her poisons, and only serves to inflame her mana problems.
That leads us to W and R. W is effectively useless, even with the amp. 13 damage amplified by 20% barely breaks 15 damage. Almost all champions can soak it up and ignore Miasma entirely. This is a problem, especially when we have other champions like Teemo, Singed, and Twitch who have more effective poisons than she does, the poison mage. That's just wrong. R has major issues in that there is a cast time. No one else has this weird, uncalled for cast time on a spell like this. Unlike champions like Zyra, who has a projectile multitarget root, Cassiopeia has a point blank stun that is akin to Lissandra's W and shouldn't have a cast time. Why does her looking at someone have a cast time? In so many instances where her R should have saved me, it hasn't, because that uncalled for cast time has given the foe too much time to end me. An ultimate should be an ultimate, not some gappy low rate spell that is easily thwarted; this especially since Cassiopeia has to be point blank to use it. Please fix it.
And finally, one other major issue with Cassiopeia is her death animation. On every single skin other than Jade Fang, when she breaks apart, the model reverts back to the old classic model. Fix it. This has been an issue since well before her rework.
As a reccomendation, strip E of all of it's bells and whistles. Return it to it's pre-rework state. Drop her passive, give her ratios back to her Q, W, and R, and give her a new passive. Here's my suggestion:
Whenever Cassiopeia kills a poisoned unit, she gains 1% of her max mana. Every fourth spell cast has 10% spell vamp.
We simply want Cassiopeia to be a poison mage. As in a mage who's sole purpose is to cast poisons at people. We done like an E focused kit. Please fix her.