Since the previous round of Marksman changes, I always thought that the IE was pretty much mandatory for any AA-centric marksman. The crit damage modifier and high AD were simply so good that reserving a slot in your inventory for the IE was almost necessary to dish out enough damage in teamfights.
I'm glad, then, that they're finally addressing this in preseason by nerfing the AD you get down to 65 (which is even lower than what I believe was its value before at 70). However, now that there appears to be easier access to crit items, I'm not sure if this is enough for it to be a situational rather than compulsory buy. There's nothing, for instance, stopping someone from buying both Essence Reaver and IE; the preseason site boasts the Essence Reaver and BotRK as competitors to the IE in damage, when (I feel, at least) they are probably supplemental.
I could be wrong, preseason hasn't even arrived yet, I'm open to being wrong. Still, **the fact that the IE can stack with these other big items, in addition to the multiplicative nature of its damage, means that the IE had to be nerfed to compensate for these situations.** I'm not sure if the IE can ever be a situational buy in its current state.
Here's what I think:** We should make a "Crit Modifier" Unique Passive** that each of the "damage items" (according to the preseason minisite) has. However, each one would modify Critical Strike in a different way. The Essence Reaver would return mana and give additional CDR, IE would increase crit damage, and BotRK would deal %health per crit.
By making each of these passives un-stackable with each other, you could requisitely buff each item because you eliminate the situation under which you buy them with each other - plus, it makes Critical Strike a more interesting investment and allows marksmen to buy situationally. If you need to tankbust or need the CDR/mana, for instance, you have to forgo the IE completely; if you want _Big Crits with IE_®, you have to rely on the new Giant Slayer item to eat through tanks, without the help of the BotRK.
I recall certain Rioters musing that they would like to make Critical Strike more meaningful than "moar pewpew"; I feel like this would be a good way to do that.