Elise just got gutted last patch, and it was pretty painful. As an Elise player, I can tell you that nerfing her numbers really hurt her jungle game. She might still be viable in top lane, I don't know. Her clear speed is much worse now, and it will take some time for her to adjust. I'm not sure she can recover without help because I feel like a lot of her old power was invested in numbers. She's one of my favorite characters, so it sucks to see her nerfed.
I think she's probably still OK, for the record. Her kit is still very capable of securing ganks, although Riot hit literally every part of her kit at once. I feel like the difficulty in ganking with her is not worth the power she now carries, though. There are easier junglers now that do better (lol Pantheon).
Lee Sin is next on the chopping block. Let me start by saying I'm nowhere near as emotionally invested in him, and seeing him nerfed would be good for me since I don't like playing him. The big problem is that Lee's kit is so good that it will be hard to nerf him enough. He's a simple case of completely busted powers with huge base numbers. It is super hard to get away from Lee. His dash kick > ward hop > kick enemy into team combo is so ridiculous that there's no real answer except for flashing ahead of time. The term is "insec mechanics," after incredible Korean player inSec. Lee Sin is a character with tons of theoretical depth. His abilities allow for all manners of crazy antics that weren't originally intended when he was designed.
I will go outright and say that a character that works outside the developer intentions of a game is probably bad for an esports game that is in continuous development. If the game is finished (like most fighting games), having something imbalanced is OK because it can either be banned (if it's actually OP) or people will figure out counters and the meta will stabilize around that. Super Turbo, for instance, has a really stable meta and the top tiers aren't 100% dominant. People still main the lower tier characters and do well with them because they understand how the top tier matchups work out.
In a moving game, introducing new elements or tweaking balance means that things like Lee Sin (with versatile kits and weird interactions) continue to be dominant. It's even more so in a MOBA where there are fewer options for any given character.
But Lee Sin himself? Is his kit that broken? I think the answer is no, but I do think he should be nerfed. I don't think the nerfs should be what he's getting, but I appreciate that Riot is trying. I don't think that comboing his passive is really going to pan out in high level play and the nerfs are straight nerfs. I think that numbers should be reduced on his dragon kick (it's way too high, so nerfing it is fine) and the kick length should be reduced. I also think that increasing the cost or cooldown on Safeguard if he hops to a ward is fine. I think they're specifically targeting the QQWR combo with that.
Ultimately, Lee Sin's nerfs are like any nerfs, there's going to be adjustments and it's probably fine. I think that most people who wear the designer hat and are informed about his design think that it's too much. In the local sense, he'll still be OK and probably viable even in high level play.
The problem is the jungle meta is... sort of fragile right now. I think that junglers will continue to need to be nerfed until a fix occurs. Pantheon is too good, and pushing him up is probably not good. I don't think we need to see a League of Evelynn again and Kha'Zix is also a problem that should have been addressed in Season 3 when he launched in a completely broken state.
Currently the top tier of junglers are all so busted that Vi is considered second tier. What kind of jungle is this game that has Vi as a second-string when her ganks are practically inescapable? What hope does the other, weaker junglers have in a meta like this? I think that nerfing junglers is potentially bad just because it will polarize the other, easier junglers more. I like that Lee and Elise are hard and give great rewards because Pantheon is too easy and gives great rewards.