I'm sorry but I just don't hate Rengar, nor do I think people should.
I anticipate some downvotes and arguments, but I hope some people will see my point.
Small rant incoming, but its broken up for ease.
So Rengar. First of all, let me say that I am in Silver 3, and by no means am I an expert on this. Most of my games recently I have been playing Kha'Zix, a lot of which are usually against an enemy Rengar jungle. Look up SlayerTay6 on OP.GG or lolking if you want the winrates against him, kda matchups, or anything else. I have never had issues in a Kha'Zix Rengar matchup, with the exception of the Rengar being outright fed, which every champion can dominate when fed. I feel like he actually has some key weaknesses that people need to use against him. Gonna say it now, Rengar is not overpowered or opressive.
(DISCLAIMER I AM NOT SAYING TO BUFF RENGAR)
Rengar's Q: This actually has some pretty bad base damage stats at early levels. Compared to a lvl 1 dmg of 70 on Kha's Q, it's substantially worse on early clears. I've never had trouble skirmishing with a Rengar at early levels in the jungle, unless he has a clear advantage of another person, health, or I was being an idiot and fighting next to a bush.
Rengar's W: The resistances I think are fine. The damage might scale a little too much with AP (although I've heard AP Rengar is fun). The healing The healing, on the other hand, is different. His healing increases by the amount of health missing. Most Rengar players (to my knowledge) use empowered W often. You have to be smart when facing a Rengar who uses empowered W. What I usually do is use burst to take out a good amount of his health and make him afraid. Usually a Rengar will back up into a bush for a jump, but if you kite right or fight not near bushes, you can avoid a good deal of his burst. After that, try using a CC if you have someone with you to stop him from using empowered W. Then you can use your burst a second time to finish him off.
Rengar's E: An appropriate skill that does what's needed. I do agree that the AD scaling on it is a little much for a primarily CC utility move, but it isn't a lot when you look at all the numbers as a whole.
Rengar's R: Oh boy. This is what most people are complaining about. The "I got killed in 0.01 seconds" posts are all over the place. I recently played a game as Twisted Fate and was camped by a Rengar. I played safe, waited out the camps, and farmed. By the end of the game the Rengar had neglected he rest of his team and screwed over other lanes, which helped me catch up. I built a zhonyas. The death recap shows you the time from the damage dealt to your death, not his travel time from the leap of Rengar's ult. This means there's actually a good window of opportunity to react. I think there was one time that I didn't zhonyas in time, and that was because I was trying to talk to a friend of mine sitting behind me. Without his ultimate, Rengar is near to useless in mid to late game fights. If you time your engages right after you know his ultimate is down, it is really easy to play around his cooldown (even though it is low) and force a fight that is essentially a five on four (or 4.5 if he's building different than burst).
Oh, and try this trick when you see the exclamation points. Have everyone all of a sudden run towards each other and group up as tight as possible. He will most likely mess up the clicks or get cc'ed. (at least in my ELO)
That's my opinion. Rengar is good for assassination, but horrible if you play his weaknesses smartly and fight when you are strong, not him. As long as he isn't hella fed, which is surprisingly avoidable if you play cautiously, Rengar is most likely not going to be a threat. Again, I'm not an expert and have actually not played Rengar myself, only a good deal of Kha'Zix games. If there is something I am missing entire because people in my ELO are just not mechanically or decisionally good, tell me and I can revisit.
The boards are overwhelmingly swayed by a few opinions, and I feel like people find it easier to agree with the "x champion is x" threads. Take a step back and look at things as a whole, and decide for yourself your own opinion ^.^
**Edit: **
Lovely Pants made a good observation that vision is still being looked at and will probably result in trinket changes, meaning Rengar and other champions who rely on lack of vision may be indirectly nerfed.
Vicarious117 mentioned that most of this post applies to assassin Rengar, and is different for bruiser or tanky.
and you're playing ADC or a squishy Support - you're fucked. Period. There's nothing you can do to stop him from 100-0ing you in at least every team fight if the Rengar is played by a semi-concious human being. That means you will always have to rely on your team to take him out quickly and win the 4v4. And we all know how fun relying on your team is in Yolo Queue.
for AD champs. Death's dance is about as much as you can get to, and thankfully that is being buffed. Sadly it isn't necessarily an ADC item.
as a third main item and don't get
till later in my build. Not sure if this counts as more bruiser-ish, but Kha can build a little bit tanky to an extent.
would be the first 2 items