It's mostly a utility item.
With blue builds it gives +10 AD when paired with Muramana or +15 AP when paired with Seraph's Embrace
That is very unimpressive considering how expensive and time consuming it is to get both items.
The armor is not all that useful since Ezreal typically doesn't build much if any bonus health.
The +20% CDR is honestly what utility the item gives that is the most important on Ezreal.
The sheen effect is very useful, don't get me wrong, but +100% BASE AD is not all that overwhelming. It used to be +125% which was much more powerful.
Yes, the slowing effect is annoying, because Ezreal is typically able to proc it every time, and he is already very slippery to begin with.
HOWEVER, .. that is the way that Ezreal is supposed to be.
So here is the deal, .. when you see an Ezreal buy a Tear of the Goddess, ... tell your jungler to gank him, .. and camp him. Make him useless.
He can't stack his tears when he is dead, and he will never get around to picking up his Iceborn.