Unfortunately League has been in a downward spiral lately. Although to me it isn't the meta changes in the patch that did it (I actually like the faster games although it is a bit too fast).
1. Bugs. I can tolerate a few bugs but lately it has spiraled out of control. The Karthus/Taliyah bug is very strange to me... it is clearly known by Riot but they still don't disable Karthus/Taliyah for some reason.... why? Karthus is what I consider my main and I have had numerous games on this account and my other lower ranked account vanish into nothingness like the game never existed. Every time this has happened it has happened in my promos right when I am about to win. I feel like they are letting this bug be abused for some reason so certain "booster" people can end the game if they arn't winning. I won't say more but I think this is very very very very odd that they have not disabled Karthus and Taliyah ingame. On top of this you have the FPS lag with the anticheat update... how did they not know it was destroying a fundamental aspect of the game and making people have extreme FPS lag?
2. The general behavior of other people ingame. I will admit this is not riots fault but their system that only bans based on chat words is very exploitable as we all know. Additionally I think the ragequit/trolling attitude is so widespread in the community it is probably impossible to stop. It is made worse by the concepts of promos and "this game doesn't matter". Additionally how certain regions don't get banned for toxic chat but NA does.
3. Matchmaking. I don't mind unfair games but I do mind if I get unranked players in my Gold promos when I am against a full Plat team... they don't know how to play the game and I even suspect some are bots and not real players.
4. Ranks. I have never intentionally dodged and I mostly play solo que and this puts me at a severe disadvantage compared to anyone else in the ranked matchmaking system. Sadly due to how they have designed League with the attempted forced 50% win rate dodging trolls or bad players on your own team is the most effective way to gain mmr unless you are dou quing with a high mmr smurfer with strats like Karthus/Nunu or Yi/Tarik or some wombo combo type concept.
5. Win trading/smurf "gatekeepers": It is one thing to make a game hard to win. It is another to have this going on. I will admit at my lower elo it isn't that bad compared to higher elos but it is a huge problem that even streamers encounter at the highest level of the game that makes the ranked ladder biased towards people who achieved a higher rank earlier in time then others. It is no wonder NA is bad at worlds when the NA ladder is probably the most messed up due to this. It takes hundreds of games to get to Plat/Diamond, and many people don't have the time for that and the stupid nonstop trolling stuff that happens at lower ranks.
6. The general lower skill ceiling of AD champs verse AP mana reliant champs: Mainly because even if AP champs play a game perfect they cannot deal as much tower damage.
7. Infernal Drakes and Wind Drakes drastically altering a game. It wouldn't be as bad if it was just one but often it is two or three of them in a row.