Before the age of Keystones
What I miss the most in League of Legends is the old rune/mastery system. Back then the runes were just a small buff for laning or so, but now they can be game changing. Especially the addition of keystones. The fact is, some champions are able to abuse some keystones, while some are not even able to find one for themselves. Because the runes back then only gave base stats or things such as gold gain, they never felt like they were breaking the game. Not once did I think back then "Man, that rune xxxxx sure feels a bit opressive", but now I seem to think that very frequently.
Not only that, I think the runes and masteries before made the game a bit more interesting, and fun! You could try tons and tons of new rune combinations or even go full meme mode and get full gold gain runes. Now the runes just mean too much for the game. Having that conqueror on Jax or Riven is so important now that it makes me feel a bit sad. Were runes really meant to change the flow of the game that much?
Still, the worst thing about the runes nowadays is the ability to create such a huge gap between champions in terms of strength. Sure, even before the addition of keystones there were champions that were a bit oppressive, but then we knew for sure that it was the champion that needed fixing. Now it's a big complex thing of is it runes, or the champion? Nerfing the runes could mean making many champions much weaker, while nerfing the champion could mean a complete exile from ranked games for that champion.
I really, REALLY wish that the Runes didn't mean so much for the game. It just seems to make the game so much more imbalanced and honestly, not fun. I also kinda miss my greedy goldman GP build for when I'm bored.