I don't know what's going on, but some champions, such as Riven, Yasuo, Jax, Fiora (etc- mostly AD bruisers) are really strong / much stronger than before.
Yesterday I played against Jax, who was in jungle... My team was ok, we had advantage in everything - kills, turrets, dragons...
I was AD Nidalee top and I easilly killed Jax in 1v1 fight, since I was destroying the 2nd mid turret and he jumped to defend it. I was like ''ok, we will win this easily'' (since he was the best in enemy team). My team destroyed bot inhibitor and the 1st Nexus turret, but they had to go back, since enemies respawned.
Jax wasn't even fed, he had some more kills than deaths, like almost everyone in my team- but all of his team-mates were almost useless.
I killed Jax in 19th minute. 3 minutes later, Jax, who previously took just one kill (just like me and my mid-laner), managed to kill me and Yasuo 2v1 and then to jump on Tristana and to kill her as well. I still don't know how, but ok, we still had advantage (destroyed bot inhibitor, etc). It was 24. minute.
Around 26-27 minute, we pushed our lanes and prepared to take the 3rd dragon. Jax came and literally deleted all of us with his abnormal attack speed, damage, stun... Took 4 kills in a row, took the dragon and mid inhibitor. We respawned, focused him and he killed us again, ALONE. Took 11 kills in a row, in less than 2 minutes. Is it normal ? And of course, destroyed everything in our base in 2 seconds and won the game. He was 7/5 or 8/5, but in the next minute 19/5.
It wasn't my team's fault, we simply couldn't kill him, even together, even with more advantage, but he easily deleted all of us.
I've been playing LoL since preseason 4 and I haven't seen something like this before.