The changes on Rengar are full of garbage
before the rework. Rengar was seen as an unhealthy champion due to the fact that he can burst you instantly in less than 1 seconds on invisibility. Riot decided they are gonna change his burst and make him "harder" and fit in the hunter theme he has. That is absolute garbage talk right there. I've hated everything about this rework but only a few things.
Passive - Rengar's bonetooth necklace before rework is kind of unhealthy due to the fact that you could kill the same target and getting better and different results. That didn't fit his theme and it was unhealthy. Riot reworked the bonetooth necklace to be kind of like the bounty hunter in the masteries. Basically kill 5 different champions for better rewards. This is one of the things i like about this rework. How you can hunt all the targets and get benefits from them. I liked the killing the whole 5 people change, one thing i didn't like about this is the rewards you get. Seriously, The rewards are stale and it's basically +AD. It should've been more utility based not damage based like the old bonetooth necklace rewards. Maybe change the rewards and give him like for example, if you kill the enemy top laner you get longer bola range or longer root duration. The Ferocity is very unfitting for an assassin like Rengar. Why does it decay? Why does it have to be an in fight mechanic for an assassin that's supposed to be hunting and killing you instantly? It doesn't fit him. Ferocity was always a preparation tool for pre rework Rengar but now it's an in fight mechanic. It just doesn't make sense, just bring back how the ferocity is a preparation tool. ALSO, probably one of the reason riot removed the preparation on ferocity is that YOU could lock down the target after you jump with E, I suggest just make your ferocity decay instantly when you go full stealth mode.
Q - this ability looks like it's a good fine ability for an assassin like rengar. I thought before the rework that it would be fine and people in PBE are just whining about how they cant use this ability correctly. I was wrong. This ability is very clunky and the animation takes too long for a champion that is supposed to kill you fast in 1 second. It is basically a main damage ability for a bruiser champion if you just gave it high base attack damage.
W - this ability is also now a bruiser ability. This is now an ability for dueling and surviving the jungle rather than helping you kill your prey and survive through it. It doesn't make sense for an assassin. Rengar's ferocity bar encourages spamming your damn abilities when you land to the target so you can get off your 4 stacks ability. But this just gives him a choice between surviving or having more and better next ability. The old Rengar's W didn't make a damn sense but this didn't make sense for an assassin either.
E - this ability is fine like it is. Riot just made it worse by reducing it's numbers. It's fine because Rengar can get a fuck ton of attack damage. I don't see a problem in this ability except one nerf that needs to be reverted. His bola's delay should be removed since Riot made it so that Rengar couldn't just lock down a damn target after his ult (pre rework rengar). But why not revert it. It's fucking clunky as hell.
R - this is the biggest cluster fuck of Rengar's kit. Why does it have to be camouflage when this encourages you to position your damn ass to mark the high priority target like ADC which is hard enough because camouflage reveals you when you are near? Why is the indicator so damn high? Why is the Hunted/Marked target critted when you jump. It has no sense in it. Before the rework, i thought riot made his ult kind of like.. Kindred's marking. But it's just utterly garbage. If you wanted this to be camouflage, At least make the hunted target be marked on the side like kindred's. If you wanted HUNTED to be the nearest, WHY CAMOUFLAGE...
TLDR : Rengar's rework made him clunky as hell and only few of the changed things support his theme as a hunter.