I personally like the rework. Whenever I played old Cass, it always seemed like she was only good in lane; she was a bitch of a lane bully. But as the game drags on i feel like she loses power and isn't really strong. Though Cass may have lost some damage with the rework (which I think she does slightly more damage later on due to her new passive), she gained a bunch of non-damage utility buffs that I think made up for it. Most of it has to do with her passive and I reach the cap typically by 30 minutes, which is usually at the cusp of mid to late game transition.
A major one if the fact that she gains mana back upon killing units with her Twin Fang. Cass imo had problems wave clearing because she would go oom with all that poison spam and twin fang spam on minions to push down a lane. Now as Cass i can push a lane down in like 3 seconds and still be full mana and thanks to the heal on twin fang, keep her health up.
Additionally, the heal on her twin fang is pretty good buff too. Since Cassiopeia is a mid range mage, she's bound to be near the action. The heal is comparable to the life steal from an adc, who typically take bloodthirster as their only life steal item. Late game, let's say ADCs hit for about 300, which is unlikely as many people have some kind of armor built, and crit for 750 with an Infinity Edge. This means they heal 60 and 150 on crits. Late game Cass can get over 1000 ap, allowing her to easily heal 100+ each Twin Fang and with the reset being half a second, she can heal 200+ within one second (technically she can hit someone 3 times within a second, the beginning at 0 seconds, second at .5 seconds and third at 1 second putting it at 300+ heal per second)
I like that they made the it 20% increased movement speed at all ranks on her Noxious Blast. You lose 10% bonus movement speed at full ranks from how it used to be, but most people (for me at least) take Rylai's on her and if you aren't catching up to someone who's hit by a 15% slow (and later a 35% slow with twin fang) in conjunction with a speed boost you're never gonna reach them. Plus the higher boost at early levels is great in lane to give her a bit of flexibility and ease at playing aggressive in lane and fleeing.
Though I feel like Miasma's damage got cut a lot, it's a harmless change really. No one ever stays in Miasma long enough for the damage from it to be noticeable. I find that Miasma is best used for its incredible strong slow and since its quite hard to dodge upon cast because there's no indicator showing where it will land and Cass "spits" it out quick enough to where it's almost instant cast time too. Coupled with its long range, I use it when I can't reach someone with simply a Q to close the gap and need to slow them down a bit so I can land my Q and begin the Twin Fang spam train. Miasma's near unavoidable status makes it a great way to poison someone while Noxious Blast is down or if you missed your Q.
They lowered the damage on her ult a bit but they lowered the cooldown a crap ton too. Her ult is pretty much guaranteed to be up for every single fight or skimisht, back to back, mid and late game. This is thanks to her passive at the lower cooldowns too! Her ult is up a little less than 40 seconds sooner compared to her old ult, as you can easily get 30% lifesteal with 5% cdr mastery and 25% from her passive.
I enjoy the new changes that her passive brought, ever since the changes I feel like Cass is a lot more noticeable late game, with her heal, I was a able to 1v3, chunk even the tankiest champion with 200+ magic resistance, and a great side lane pusher and duelist. People say they don't like the stacking mechanism, but all it does is reinforce her poison gameplay, despite everyone whining about her losing her "poison identity". Even with old Cass, it was never about throwing out your poisons and watching your enemies slowly die; it was very clear that she was meant to poison, leading to a Twin Fang spam. If she was all about poisons and thats where the bulk of her damage came from, what was the point in using Twin Fang. That's why Twin Fang is her main damage source and why it requires poison as a prerequisite to spam. That way, her kit has cohesion and each spell has a purpose in her rotation. Riot wanted to move away from just throwing out Miasma and Noxious Blasts as tools of poke and siege and thus shifted a lot of her gameplay into Twin Fang. Plus her attack patterns become easier to read and ushers in better counterplay. Simply standing in the back and throwing out poisons leaves much to be desired. Riot wanted her to be a high action and high skill cap version of Anivia and I think they succeeded in doing so. She revolves around starting an engagement with her poison, then proceeds to assault her prey with Twin Fang while they're poisoned. This fits her as a champion really well imo. It really conveys the idea of a snake who has struck you with its poison, weakening you and lunging all in with its fangs for the kill. Plus it fits her lore well too; biding her time, waiting for the right time (like when someone is poisoned in game) to attack and kill (in game this would be twin fang spam) sivir in order for her to reach her goal of unleashing renekton and xerath and being turned into a snake (if that was her desire).
