Zed didn't get a nerf, it was a shift in power (Slightly still a nerf though)

Zed Razor Shuriken (Q) Base damage lowered to 70/105/140/175/210 from 75/115/155/195/235 AD ratio reduced to .9 from 1.0 Damage on Multi hit on same target changed to 75% from 50%

Death Mark (R) Proc damage increased to 30/40/50% from 25/35/45% AD ratio lowered to .5 from 1.0

Essentially these "Nerfs" mostly just shift his power to being more combo oriented. It lowers his power in lane by quite a bit unless his opponent is dumb enough to be hit by both Q's every time his W is up (Which then is your own fault). But even then Spamming Q's vs the Q W combo, Spam Q is better so, its a nerf ever so slightly.

Then the change to Death Mark is a shift in power same as the Q with an ever so slight nerf if you dont land them ALL. He'll do a bit more damage in return for landing all of the Q's, not by a lot (The actual math suggest by like 3% extra..) If you land both Q's.

So throwing all of your Bia's away about Zed being insanely OP (Data suggests not), he got a shift in power that seperates the Bad Zeds from the Good Zeds. Good Zeds will get a slight reward for pulling off good combos while bad Zeds will suffer dramatically as no longer will they win just because of being oppressive (Which is what wins Low ELO games 99% of the time).

Great changes in shifting power with a bit of small nerfs added in as well, if you don't agree well thats up for debate.