Nidalee Balance
I used to play Nidalee a lot before she got changed, and since then I've only played her about once. So I'm not sure as much of how it is to play her, but as far as playing against her... yikes. So many games I have seen her build straight tank and still do more damage than anyone in the game. (And of course be unkillable besides). I have yet to see a Nidalee do poorly, especially as AD tank. It just seems a little unbalanced to me.
I also don't like the fact that since the change, she's completely different to play. No more AP Nidalee- that just doesn't work anymore. AD Tank is the only way to play her, and it's OP.