These threads on him are absurd.
A few people touched on exactly what he is, a counter to the current "I only want to play a melee brusier top" - thats why so many people are whining and crying about him, because 3/4th's of the NA server has a massive hard on for insta locking a brusier top.
Pick a ranged champ, (Kennen, Nid, Swain, hell even Vlad) and go to town on him from ranged and absolutely destroy him. Last game I was Ahri mid and our Irelia died to him twice in the first two minutes so I lane swapped with him and absolutely wrecked Darius (this was just a bad Darius who got overconfident, not a counter)
He kill steals like a boss, but there are so many CC options to use on him that past 30 minutes when he has 80% of the teams kills and their AD carry has 1- pop a randuins and a exhaust on him and GG, your carry will kill him before their underfed carry kills you.
TL;DR he isn't OP, he just wrecks the current meta (want to play bruiser top- you lose), therefore he is OP. Same deal with Shaco- no one wants to buy wards, so he wrecks. Get over it.