Death's Dance just looks like bad design
An ADC's primary weakness is burst.
Death's Dance reduces all burst by 20%, applying the damage as a DoT effect over 5 seconds instead. This basically means you'll need 25% more damage (1/.8) to do the same amount of damage in the same amount of time. And 5 seconds is ample time for the ADC to get out of any CC they might be in and just lifesteal back up, especially now that Mercurial Scimitar also gives 10% lifesteal.
Then there's Phantom Dancer, in case 20% isn't enough. PD now reduces all damage from the last champion hit by 12% on top of giving 12% movement speed. That's effectively 32% damage reduction for any burst, provided the ADC does any damage within 10 seconds of that burst of damage.
Riot, why are you insistent on removing this class's primary weakness? They're supposed to be glass cannons, attacking safely at a range. Not a class that can have infinite sustain, tank burst and deal the damage they deal all at once.
is getting most of her kit removed. 
got his dash thing nerfed.
now has a reload sort of thing on his auto attacks and people can block them. 
is basically the same but now her traps let her head shot from bonus range. 
got his attack speed nerfed. 
is nerfed even more. 
might get small buffs 
is still one of the most irelevent adc in the game 
is the same but now she isnt auto criting.
is the same nerfed self with a small reset to his stealth thing.
sounds broken just a little but now he is rooted by his auto attacks during his attack speed buff and deals 50% of his ad in his autos during the attack speed buff 
got small nerfs and that's about it the only adc that hasn't changed much is 
but he got his Q to reduce his spells by 1.5 seconds instead of 1 second but he benefits a lot from a lot of the item changes oh yah 
got a small buff to his ult but thats about it