Renekton doesn't need a buff, people just need to learn how to skill level him. I found a skill build that works quite well with him and I did fairly well. The problem is simply everyone was just putting points into random abilities and expected to do well. Thats like maxing out Veigar's stun and then putting 1 point in primordial and another into baleful strike. Lulwut
Mana regeneration runes hit me hard, considering how Mana Regen / level, and armor pen are generally the only runes I really have, and after armor pen got nerfed they're now nerfing this too. Sucks.
Doran's items needed a nerf, and I've felt this for a while. However if they make it to expensive to get a potion + doran's item all people will start doing is start with either Cloth/ 5 pots, Null Mantle / 2 pots or boots / 3 pots. The fact is going straight out damage early on at level 1 is fail, considering how easily bursted down you can be by things early on.
Nerf to Doran's will result in characters that can self heal will become stronger / more wanted (ex: Tryn, soraka, taric.) and will also make it so the gap between melee and ranged in lanes will only further increase. At this point in time if you're a melee and fighting vs a decent ranged and you try to last hit 1 creep, you have to expect to lose minimum 200 hp just to kill it.