So, the AP item changes got me thinking about ADC items...
Which was not a good thing. Because there is an issue with ADC item balancing: AD casters. You see, if we were to remove crit and offer lots of AD to ADCs (in the same fashion we offer lots of AP to APCs), then AD casters would dominate and not fall off late game. They would all become extremely powerful. So Riot keeps crit around to split AD champions into two groups: casters and auto attackers.
So then I started looking at the build paths for any given ADC (we will ignore corner cases such as Blu Ez and such), and what I saw was a very limited selection.
So ADCs will pick up two crit items:
and either
or
based on their mobility. There is little to no choice in the matter.
For lifesteal, you will get 1-2 of 2-3 options:
,
, and
if you have mana issues. Again, little to no choice in the matter, these items will depend on champion picks
and
are must buys, and there are not very many options to replace them (
comes to mind...maybe)
For defensive items (assuming you got only one lifesteal item from your 2-3 options), you have two options:
or 
This is surprisingly limited, wi over half of your item slots being used for must buy items, shared across over 85% of all ADCs, and even when other options are taken, that pool is usually only 1-2 additional items.
Contrast that to a top lane build, there armor items include:
,
,
,
,
,
, just for one resistance type. (Also almost every boot with every boot enchantment is viable on almost every top laner)
Edit: lol, this was posted less than two days after the relaxed new tank armor items. I think this might warrant a whole new post...
So I think that ADC items need a rework similar to the APC item rework, where every item brings similar levels of damage while provide a unique utility that the player's can choose based on team comp and play style
as you could still hit 50% crit chance if need be.
or allows you to sit on
and focus on completing other items first.