Let's Discuss: Zhonya'd Ults (Fidd, Ken, Morg, etc)
I would like to hear everyone's views on this. Why is this a good thing to have in League? And why isn't it a good thing to have in League? Consider this, like a point and counterpoint argument. Obviously, it's good for squishy champions who want to build as much damage as possible, without building much defense. This is great for teamfights. But how fun is it to Flash, Push R, then Zhonya's, and just sit back and watch? You aren't actually PLAYING the game. You aren't actually doing anything while Zhonya's is going on, except contemplating your next move. I feel that, in late game, this basically your champions entire role. Wait for a fight to break out, hit R, and wait. By then, your character will have so much damage, that you will just annihilate the enemy team. If they are not set up in such a way to better split push than you, then they will inevitably fall unless you make a big mistake. You can even look at it from a 1v1 standpoint. In the case of Kennen, his ult lasts longer than Zhonya's, doesn't it? So, he ults, Zhonya's, gets out, and if you aren't dead, then he has the movement speed and CC to catch up and finish you. It is 100% required that you have the burst and/or CC to keep him from doing ANYTHING whatsoever. Because if you give him time to push R + Zhonya's, then the fight could very well be his, unless you are super tanky, or have the mobility to get out of his ult, and the mobility to catch him once he's done.
I'm not trying to sound excessively negative. I really do want to hear the positives (from a gameplay balance perspective) in regards to this, just as much as I want to hear the negatives. In my personal opinion, I think it's anti-fun. And it really take away a need for you to have to plan your attack (as the ult/Zhonya's character). It requires an lot of strategy to counter, and typically good team communication too. And I do enjoy playing champions like Fiddlesticks and Morgana, and I do rush Zhonya's on both of them when I play them. But honestly, no matter whether I'm on the giving end or the receiving end, it feels cheap to me.
TLDR: Is Zhonya's/Ulting balanced from a gameplay perspective? Point and Counterpoint.

because they will wreck you.