1. Damage is too high. Overall. People here oneshot with 3 abilities which wouldn't happen in S5 except for overpowered champions (there were always 2-3 broken ass champions that were permabanned).
2. Too many dashes. It makes playing champions without dashes too risky to pick. You get out of position once and you are dead (wouldn't be a problem if damage wasn't this high).
3. Meta is favouring high mobility champions which makes the game more action based than tactical.
4. Inting, afk and trolling is even more often than it was in previous season, even tho punishments are increased and banning rate is higher.
5. Some champions have skills that are undodgable, which makes the whole design of them questionable.
6. Self-healing on some champions is disgusting (mostly Kayn, he ults you and is full hp again).
7. Cdr are too easy to obtain, so we don't sacrifice anything (i would prefer cdr to be more for supporting characters than for basically everybody) people walk with 40-45% cdr every game. Sometimes after 2 items.
8. Crowd Control skills are too long. In damage meta getting stunned for 3-4 or even 5 seconds means that you are dead. (again, wouldn't be such a big problem if damage was lower)
9. Scaling is too important (if you buy one ap item you might as well go full ap), in previous seasons we would get some mr or ad on a mage to survive longer or be more useful. There were more variations of builds.
10. Jungle is the worst role (nerfed hard) and boring (reworked into a weird crab hunting minigame) but for some reason it has the most impact over the games so a bad jungler can lose you a game.
11. Early game junglers have a lot of pressure and can decide the games, while mid-late game junglers don't exist because playing them is basically inting (if you don't play an early game jungler your team will be 0-10 before you even clear your camps and get level 6)
12. Ap items are not diverse at all. They are just there to give stats (except for zhonia, which is a badly designed item and should be removed) (basically an "you activated my trap card" kind of item)
13. Ad items do damage on their own which is why Shaco ended up in such a bad state (Duskblade does damage instead of just giving stats and maybe having an active use just like other items of the sort, i can tolerate Triforce tho)
14. Adc meta doesn't budge. Some champions are left to rot and others are slightly overpowered (Jinx is an exception, she is not slightly overpowered but massively broken, I love her but I usually don't play broken champions, it makes me feel like I don't deserve to win)
15. Mordekaisers ultimate makes some champions unable to even get close to him (they are dead if they do, because 1v1 against him is too much for them, looking at Twitch here but other champions have similar problems with that ult).
If you disagree just write it down. Downvoting only closes the topic, which is important and should be talked about more often. Ignoring problems doesn't solve them.