Guess which champion got buffed again
Definetly not 
Definetly not 
The important thing about Yi is that his ability to totally crush is VERY dependent on Enemy HARD CC Potential. Basically, if you want to play Yi, try to get someone to last pick him for you.
ONLY Pick Yi, if there is not a lot of hard CC.... so for example, don't pick Yi when you have a Midlane Ryze, and A Morg / Lux/ Blitz Support etc Anything that has Hard CC is going to make it hard for Yi.
On the other hand, slows are not a problem for yi.
If you do pick him anyway, get QSS to remove the CC and you can continue your Ult.