Nidalee is still stong. She wasn't that good out of diamond before and won't be it, because you need to know what you build and how to play her.
Gragas is also still good. They could reduce the W costs a bit back, down to 20-25 and I think he would be fine.
Lee Sin is still the most picked jungler in the competitive scene. Higher win rate and higher pick/ban rate at the WCS than K'Z, and that means something. His overall pick rate is also one of the highest in teh game. 45% win rate in ranked with a more than 30% pick rate doesn't say much. Take 20% of these 30% away (the worst 20%) and you get a 10% normal pick rate with probably a 55% win rate instead. High popularity always lowers the win rate.
Kass has a horrible early and only a decent mid game, that is all. As a late game champ, he is still awesome. Problem is that popular ADCs (I mean you, Trist) are way stronger late game.
Cass is not that bad, for a champ that is not meant to be good against the current meta champs. Syndra, Xerath, Trist, Braum, ... . She is a champ that is best in a counter engage comp or a kiting comp. She shreds the front line, so when it comes to front line vs front line (we need bruisers or tanks back top), she is the mid laner that shreds the enemies faster and she has no downtime. She also protects the ADC from dives.
Eve doesn't have a good time, but her invisibility still gives her an advantage when picked at the right time. She is not horrible, but champs like Lee easily counter her, and If she can not invade an Amumu early, he will be able to fight her all the time later and probably wins.
These champs are not top priority picks (except for Lee), but they are all still good and win games in the right hands.
Azir with his 39% win rate is a decent pick for some high elo players, and that before 4.18. High skill cap, not known by too many and has a lot of possible item builds and playstyles. Now, with all the bugs fixed and 2 pretty good buffs (nearly 10% more AS and that also from items and CDR) he could be a monster in higher elo. I don't expect his win rate to go up above 50%, but that often comes due to players trying to learn such a champ because they see streamers doing good with him.