I'd bring back stackable tenacity like cloak and dagger for start, since it's absurd how much CC is in the game with almost zero means (besides taking cleanse or merc treads) to counter it. I don't particularly enjoy being stun locked for 5-10 seconds (doesn't matter because I only live for 6 of them anyway, by amumu ults, braum knockups, jax Q and whatever else the other team throws out in the final teamfight. At a certain point I may as well just walk towards them, hit S and go make a sandwich because I wasn't going to be moving anyway.
I'd add a melee/AD version of banshees veil.
I'd scale back the early game damage on juggernauts so they can't automatically win lane and therefore the game unless I play something stupid like quinn or twitch top.
I'd make minions and towers stronger and deal more damage.
I'd nerf the fuck out of everything. Every item. Every champ. No one should have enough armor at level 2 to face tank a tryndamere to death. That's absurd, no one should do enough damage to casually walk up and three tap someone at level 1. Early game trades should be more about skill than "lol too bad I counter uuuuuuu"
I'd nerf ALL abilities and have them scale more... Take darius's Q for example
50 / 80 / 110 / 140 / 170 (+ 100 / 110 / 120 / 130 / 140% AD)
I'd make this bitch look more like this... 35 / 65 / 95 / 145 / 185 (+ 50 / 75 / 100 / 105 / 110% AD)
Abilities shouldn't be the determining factor and no one should be able to face roll and win. Period. Everything should be weaker early game and stronger late game.
Tank items should never be so powerful that a bruiser can't hurt them. A garen with cloth armor and boots shouldn't be able to afk kill someone with a tiamat, that's just absurd. Similarly a person with a tiamat shouldn't be able to just walk up and brain someone in the noodle who has chainmail + ninja tabi. It's just common sense.
Farming and income should determine who is stronger. If I can farm a black cleaver before you can farm armor or health, I should win if I have the skill to duel you down. I shouldn't just be tinking down small tinks of HP... Similarly, if you get an item before I can farm up something, I shouldn't be able to safely duel you.
A problem I see is, and this is coming as a top lane main... some champs, at a certain point, will deal so much damage even when behind on farm and down a kill or two that I end up against my tower hoping for a gank... this isn't how it should be.