Nocturne is a dumpster champion that is only viable for his ability to block ward vision via his R, allowing his team to walk over key spots undetected.
His R is extremely easy to counterplay, all you have to do is not be isolated, underfarmed, and out of position.
So basically have some common sense.
Oh theres a Nocturne? He has enough kills that he could 1shot me if i isolate myself? Well i better not isolate myself and set myself up to get 1shotted by Nocturne.
If you are a champion that is susceptible to Nocturne sticking to you after he ults, and you dont have enough farm to duel him, you need to not isolate yourself and you need to be aware of your positioning. Force Nocturne into a situation where if he is going to kill you, he's going to die doing it, IF he even succeeds.
On top of that stopwatch/zhonyas/GA pretty much make his ult nonexistent.
Hell, even Ninja Tabis basically invalidate his entire existence. He is a autoattack based assassin, which is a BIG HANDICAP.
You can dodge it if you run in the opposite direction Nocturne is landing from.
You can dodge it with any dash.
So on top of Nocturne being countered by teamplay, he's also countered by literally any kind of mobility, and any kind of defensive CD.
AND he's counterted by items that virtually EVERY champion builds.