For me it's getting people to rotate on objectives instead of suicide for kills. Not long ago something was going very wrong if your team had multiple deaths before five minutes. Now that's every game.
Seriously though, the worst feeling in the game is when you can't get your team to pay attention to drags (especially with low vision and auto filled supports not helping to ward it), and then your whole team auto loses from the combined dragon strength on the enemy team. People really don't understand how much an early ocean or wind dragon can swing a game for you.
Makes every game feel like a constant tiring struggle. Instead of getting to that one point where you're strong the game has become a matter of making sure everything doesn't fall apart on multiple fronts. Whether that be dealing with enemies who can go invisible/clone themselves/triple dash or w/e, to herald, to first blood towers, to dragons, to scuttle crabs, to getting them to group and rotate on things together.
Another thing I don't feel is well appreciated is how much "mental tax" all these new champions have. If the enemy team has a Neeko, a Shaco, an Ekko mid etc, you are keeping track of where Ekkos ultimate is and if he can heal, which one is the real Neeko, the real Shaco, Shaco's clone, the boxes he's already putting down, their myriad of skill shots etc. I'm only listing three champions here. There's just a lot to keep track of.
Oh well. End rant. I really don't expect them to do anything about it honestly.