He just seems over the top in just about every way. A passive with a 70% ap ratio and massive slow. A q for reliable wave clear, and again a slow. A w that gives a percent health, slow, shield, and a stun. An E that gives an escape/gap closer, and if that wasn't enough, an ulti that has an escape, with the added benefit of a massive nuke and heal. Are there ways to stop him? Of course. But the issue is the same with Fizz, LB, and Zed. He's just "unfun" to play against.
Too often it seems like these assassin type champions are given too strong a gameplay style. And while the safety might be annoying, the amount of cc and wave clear that someone with that much safety is even more annoying. I mean I have faith that Riot will eventually get him to a point where he's not as frustrating to play against, but it does feel like, at least to me, that there needs to be a change in how they make some of these high burst assassins to actually accentuate some real cons to their kit.