To buff Zed.
I have played him in ranked recently, jungle, top, mid and no success whatsoever.
His engage range is too short for an assassin
His damage is too low for top
He gets outtraded by literally anyone, and his poke Q is unreliable, too slow
He has low health for a top champion, and low tanky stats overall, not worth building into a tank
His passive is the most useless thing in lane, no opponents, either before or after level 6, would ever be stupid enough to stay there with less than 50% without backing or being extremely careful
So you say he is to be played like an assassin? Well let's compare him to one that is just like him: Talon (and I mean, very very similar since they both have a damage amplification charging spell, and AOE slow spell and an auto attack booster)
His burst potential is terrible, he has at VERY VERY MAXIMUM 834.375 (+125% total AD) (+497% bonus AD) + 15% max health (this does include his W's passive effect in the math, simply add his total / bonus AD to find resulting damage)
Talon has a burst of 1166.25 (+115% total AD from Q, it's an auto attack)(+508.5% bonus AD) (I didn't even take into consideration his passive because I don't need to)
For Zed to get maximum damage, he has to make sure that ALL his shurikens hit the same target AND HIT THAT TARGET FIRST, which I have never seen happen in the heat of a teamfight, where they have disablers, disengages, etc...
Talon, on the other hand, has but to press E, W,Q, R to unleash his full burst, all in a split second, with a range vastly superior to Zed's and an invisibility to top it off.
Now you may say: oh hur durr!! but Zed has + 15% max hp that you didn't account for! Well, let's do some math:
(difference of base damage) = 0.15 (total health)
n=331.875/0,15 = 2215.5 total health, which is the average health of an AD carry, which (as an assassin) you should be focusing in the first place
This means that until the max health of the opponent is 2215.5 (which means below 2215.5), Talon's base will be higher than Zed's base + 15% max HP
You can then consider the fact that his full combo will never happen at such a developed stage of the game, decreasing Zed's damage, while at the same time considering that Talon has his passive to increase his damage (don't give me **** about missing, if you miss with Talon's combos, you shouldn't even be in this thread)
You can then also add that Talon has a silence, which Zed does not (both have an equivalent slow, disregarded), that Talon's AOE is immense and Zed's is not.
In short, Zed is a very hard to play champion because of the shadow mechanism: treat him as such and make it so that high skill level people can actually do more than a low skill level (or at least equal potential)
tl;dr: Hotfix an immediate hardcore buff, just like Lee Sin, for Zed. I love Zed's concept, I find him to be one the coolest champions to play, and I think his Shockblade skin is even better than the legendary skins (props to art team, amazing job, never seen a better skin in the whole game)
EDIT: For those who don't know, Zed's ultimate 50% damage dealt thing only applies to his damage, this isn't like Vladimir's ult
EDIT 2: I also forgot to mention that Zonhya's Hourglass makes his be little more than a gap closer, besides that, literally nothing more (which means he can't focus most mages like Karthus or Diana)