The old frozen heart icon was clear in its function (looks like a heavy defensive item... is a heavy defensive item), fits its theme (frozen piece of heavy armor) and looked powerful.
The new frozen heart does not look like a powerful end-game item, does not clearly convey its function and does not fit thematically. In fact I cannot tell what type of object it actually is due to it looking more like a mage item. 
...
Looks like an icy heart nestled in a nest of more fragile ice. I'd say it looks fine.
Plus Frozen Heart always sounded like something you'd wear around your neck as opposed to wear as armour anyway.
It actually looks like a frozen heart rather than a frozen shield which was the previous icon.
It looks like some sorta staff.
Sometimes I wonder the random direction that Riot goes in.. like.. why?
I guess it looks pretty with its colors, but I can't make out WTF it's SUPPOSED to be.
The old item picture looked pretty much clear on what it was SUPPOSED to be.
