The new season will change most people's outlook on Renekton. He has great synergy with the new Black Cleaver and Blade of the Ruined King [along with a lot of other season 3 verions of items with less wasted stats]. The new jungle making early ganks a bigger risk will also give him a lot more control and the ability to play aggressively in lane like he was designed to.
He hasn't been nerf, because though powerful...The current meta he still isn't as good a pick as a lot of other tops and unlike them, he doesn't bounce back as well as a lot of other tops can when advantage is lost. He is one of the few champs that can be denied their resource, which wouldn't be that bad if it weren't so deeply woven into his kit. When losing advantage it's a lot harder for him to keep his damage relevant than some champions and utilizing his skills well pushes the lane.
All that aside, he is the flagship rage champion who has the worst generation of it. It's arguable that his dependence on it also gives him the worst use of it. That and his ultimate is horrible! Outside of the health gain, it is a glorified and worst scaling version of Dr. Mundo's burning agony...Which barely every scales if we are being realistic.
I wouldn't be surprised to see him getting a rebalance in season 3, but he will also need some love in a few areas. Realistically, if you search the forums...You will find more posts about him needing not so minor buffs over posts requesting nerfs.