The new assassins are only really strong if the right strategy is employed with them (the exception is Talon as he's almost always viable to snap your neck).
Rengar is seemingly weak if he gets pushed back early / the person doesnt use ferocity abilities properly.
Kat is rather strong but manageable.
lb is annoying if she attempts to kite or bait you.
Out of the smaller updates:
Kha is stronger than what he was but un-evolved he is generally weaker + evolutions are now all viable.
Fizz is stronger than before but his close combat cheese with his ult is less and is actually rewarded by being in combat for longer (focusing a single target).
Shaco's new clone gives him a load more power if he goes ap jungle + it's a straight up deterrent when the clone is nearby (if it pops if he's ap you're in for a bad time). Ad shaco isnt all that affected though.
-the new assassin items are a bit overloaded...
To answer a question: both lb's passive and talon's ult is invisibility not camouflage (usually the case with short duration stealth skills).
The new assassins are not broken it's more that people don't know the assassins' limits (usually really high damage but squishy) and how to react to them yet (or what to really expect from them) but that's my opinion on the matter - you'll find many who disagree with me.