Master Yi was the first champion that I have ever played in league of legends. And I have to say Master Yi now has an outrageous late game. People are saying that he is OP but I just think that if they nerf something, It would have to be Warmogs armor, his ultimate's passive, or the number of swing it takes to get double strike. Other than those things, I believe Yi is a relatively balanced champion.
These are the reasons I Believe he's a little bit more balanced.
Passive- Even though the second strike can crit, the second hit does half base damage. I just think the hits required are too small for an attack speed based champion.
Q- even though it can crit, it doesn't crit higher than a basic attack unlike say: Gankplank
W- Yi locks himself down in a stationary posistion. I've been killed mostly when GW based attacks were involved cancelling the heal.
E- Now instead of doubling the passive it adds base true damage. The passive scale is also no longer a base number but instead give you a percent of your current Attack Damage.
R- Though It's the same, it does not reset Cooldowns but instead lowers them by 18 seconds. Personally i think the cooldown reduction should be 10 seconds.
Champions that are effective are champions that have hard lockdown abilities. Also, Master Yi cannot handle hard burst: Teemo, Jax, Fizz, Tristana, Aatrox, Blitzcrank, Malzahar, Nami, Taric, Katarina, Alistar, Udyr, others among them.
Ineffective champions include those who cannot burst or have reliable lockdown.