my opinions on rengar(short version)
well I made a whole article about my opinions on the new rework on the champion. I thought people might not want to read it all so I decided to make this summary
His passive: losing stacks too often. this removed a huge chunk of the Rengar uniqueness/playstyle. basically forces you to stick in combat, not only combo/retreat
his Q Clumsy... but isn't that bad
his W overpowered when you are against hard CC with burst damage. really weak for sustain. although 50% of the damage taken is a lot. this does not fit the purpose of rengar, assassinate and get out. you are not supposed to take much damage. and if you do, you got outplayed and its natural and fair for you to die. that is how countering assassins should work right? you also usually cast all abilities right in the beginning of the engage to have empowered abilities up, so its kinda counter productive to hold your W for increased heal. if you do, you lose damage, if you don't you have 0 sustain. and if you are low in lane, you will continue being low. because your W has no Base heal, only heal based on the incoming damage. this is like a damage mitigation, a function that you expect in tanks, not assassins.
his R roaming around for rengar and twitch is not part of their plans. they don't just roam safely. they walk to a place with an objective, then go back to farming. long term "camouflage" over having a visibility perimeter is counter productive and is a straight up nerf. also, you basically can't use it to escape anymore.
suggestion: give his leap a buff that decreases damage received (like katarina shunpo) and remove the % of damage received healing form the W. make his ferocity stacks reset at 13 seconds instead of when out of combat. so you don't just remove functionality/mini game from the champion. give rengar W at least a bit of base heal, so he is able to sustain in lane, not only mitigate damage. make his Ult have less duration, and will only gives invisibility vs a marked champion. (so his allies will be able to see rengar from a distance, but not the target).
Rengar is pretty much turning into a Irelia/Xin zhao. he is losing his unique playstyle, not only the "One shot the carry" part (he didn't really lost this one tbh). 
