I'd kill for the old runes and mastery system. I'd also like to see the Utility tree completely removed and have utility added to the other mastery pages. Riot has no idea how to do utility, utility is not supposed to be an early game buff (ie; biscuit) it's supposed to be a late game scaling that's weak early and stronger later.
I'd also kill for tenacity to come back, cloak and dagger and mastery's like we used to have because it's not fun being stun/root/cc locked for 10 seconds and living through 3 of them. If a team is extremely CC heavy then we should have some way to deal with that, worst example I can think of is amumu jungle, malph top or maoi top, aniva or lux mid, ashe bot and naut or thresh support. That's a million miles of CC and no way besides merc treads to mitigate some of it.
I miss old league. I barely play and actually officially quit the game the day before the patch came out.
Tbh, I miss a lot of the old items, the runes, the mastery system, I miss everything. I miss banner of command, I miss zephyr, I miss the cloak and dagger, I miss malady, I miss tons of items that allowed you to build around a match instead of just rushing the same 3 items and (sometimes) rushing hex drinker.
I hate that everyone takes conqueror or grasp top, I hate that every assassin takes electrocute, I hate that every support takes glacial or aftershock.
Literally 80% of the "runes" don't get used. Everyone takes demo and bone plating, Legacy Alacrity, and only niche champs take anything else.
I played predator lux and got called a troll despite going 13/2 by predator -> ult snipe for bonus damage.