Best and worst champion reworks
Success:
The basic of what makes him warwick are retained. Lifesteal. Attack speed. Hunting low health targets. And the same ult, but tweaked.
Except his kit is fluid, fun, and effective. I never wanted to play Warwick before the rework, but now I find him fun to play.
I played Quinn before the rework, but I played her even more after. Her kit makes more sense now. I never liked switching between ranged and melee. Just didn't make sense from a gameplay perspective. I love being a hyper mobile assassin or adc. A very flexible champion that can do recon, flank a teamfight, speed to the rescue of a teammate, or catch out isolated enemies.
I love the new Yorick. The old one was a mess from a design standpoint and wasn't that fun to play IMO. I bought him and tried him when the rework was announced and tried making him work before the rework. I was excited for his rework, and now he's one of my mains. He's the only champion that is a legitimate split pusher by design, and that's why I love him. Split pushing is my favorite thing to do in these kinds of games. Combine that with his situational ability to 2vs1, as juggernauts do, and it's loads of fun. This is one of the few chases where I think it turned out great that they completely scrapped the old design and went with something entirely new.
I tried to like the old Urgot, but just didn't find it fun. The new one is quite fun. Although it seems stupid to me that he has dash as such a hulking mechanical beast. Must we really give dashes to everything these days?
I do miss some of the concepts of the old urgot, and wish they had been retained; like seeking missiles and teleportation.

Failure:

Both reverted. Turns out it's a bad idea to make assassins that can't actually assassinate anyone.
Zac was a champion I played a lot before the rework, but when coming back to find him changed I don't even want to touch him.
His winrate seems to concur with this assessment.
I think his Q is change is a nice idea, but it's clunky and unintuitive to execute. I end up not liking it despite it's potential.
The biggest offense here is the R change. Totally unnecessary. The old R was a lot of fun to use in the middle of a teamfight. The new R is, again, clunky and unintuitive. You gain functionality but you also lose a lot of functionality.
He's not viable in the role they intended. They had to nerf the only thing that made him playable in that position, the bonus XP.
But because his kit was too heavily designed around the idea of being an ADC, he doesn't have the flexibility needed to excel in other positions.
I actually think the current version is very cool. But anytime you have to rework your rework for the second time you're kind of forced to call it a failure.
Boring. Unplayed.
Mixed feelings:
I mained Talon before the rework. I think it's good that they kept the same basic playstyle of harass, dive, burst. And I love the parkour element. But he falls off too hard because his harass and dive ranges are too short, and he sacrifices damage to gapclose. Plus, the entire concept behind the assassin update of "assassins should have delayed burst damage" has turned out to mostly be a completely failure. Talon wasn't hurt as much as some others by this, but his functionality in teamfights is nil compared with old Talon. Low engage range, inability to get off max burst, and delayed damage. He feels even more feast or famine than he was before because of how hard he falls off if he doesn't snowball in the first 10 minutes. I think his rework has the potential to be good, but it needs a lot of tweaking to feel fun and effective to play again. Especially with the game sped up so ADCs come online so much sooner.
Swain was another one I played a lot before the rework.
His kit is well designed enough, and functions - but he's no Swain anymore. I don't like the direction they took it, because I enjoyed the draintank battlemage playstyle of the old Swain. New Swain cannot legitimately play mage tank anymore. Old swain was very unique in that regard. The new swain feels like a very generic vanilla bland typical caster mage.
I think her ult makes no sense with her kit and thematic. A poor attempt at trying to give her team utility.
I enjoyed her before the rework, but I can't stand to play her after it. Even though objectively there's some good design choices, it's just not as fun to play for me. But I know others who mained fiora would disagree.
Her anti-flash mechanic never really worked out as a bodyguard method. I miss her old kit. I don't really have as much fun on the new version. It's just a completely different champion. I never like when the rework basically deletes a character and creates a new one in it's place

, a serious little yordle, etc.
I don't have the patients to write out the three pages of info on this right now. I don't like being told to go in at certain times and the opponents knows this timing too. I just imagine designers and collaborators who go into it thinking "If we control the tempo by making players go in and retreat program-ably we not only control the balance of the game better, but it makes the game more interesting and interactive for the player". Most champs are moving to this telegraphed sequence.
and