Nidalee isn't balanced. Neither is Lee Sin.
I will cover both of these champions as they are similar in why they aren't balanced. However, let me start by saying this. They do both have high skill caps, and they both have very fun gameplay. I'm going to start with Nidalee as she is my main problem.
First off, Nidalee gets so much in her kit. This is expected (it kinda has 6 skills...) but she gets TOO much. She has amazing poke & all in potential with her Cougar W--Cougar Q. If you're marked with hunt, you're screwed. It's not right how much she has; and add this on to how low her skill floor is. That's the biggest problem, she has a ridiculously low skill floor with a high skill cap. Ther eisn't much that needs to be nerfed about her except her cougar q and maybe her spears damage.
Now, as for Lee Sin, probably one of the most known champions in LoL he has the same problems as Nidalee. He has a high skill cap, which really makes people THINK he's balanced, because you need to be "super good" with him to do well, but, it's just not the truth. You can do well at a mediocre level with Lee because of how low his skill floor is. He has two blinks, built in sustain, AoE, and he's blind with 2 ways to get vision of you. I know riot sees that he is overpowered, due to this post made by a red. http://forums.na.leagueoflegends.com/board/showthread.php?p=48101940#48101940 Anyways, I must be out.This is my first post on Gameplay & Balance, so sorry if it wasn't in the right forum. :)