Think about it like this- Clearing and ganking well could just be a matter of numbers.
A champion could have really strong abilities that support jungling and ganking but that doesn't necessarily mean he's in a good spot design-wise- Their mechanics could be overloaded, one-sided, not skillful or lacking.
Nocturne's got a ton of potential to be a scary living nightmare, but he doesn't entirely live up to it- His ult is one of the most iconic abilities in the game, in my opinion, but it's the only thing that helps him live up to its theme.
His E is an interesting mechanic and his Q is cool as a representation of the "darkness" theme, but I feel like there's something missing and those two could be pushed much further to express the darkness/nightmare feel.
His W, while a rather skillful tool, doesn't really fit his character much- It might as well have been on any other champion and it would've work the same- if not better- thematically.
-_-
I'll tell you one thing- When I first started playing this game, 6 years ago, I stumbled upon an enemy Nocturne in a match for the first time (sometime in my first month of playing) and I had no idea what he does.
Fast forward into the game, I'm in bot lane, everything's normal, when suddenly the screen goes dark with the immediate sound of many booming thunders.
It scared the shit out of me and I jumped out of my chair (and that was before he even dashed!).
Point is, I want every Nocturne ability to play a little psychological game on the player- It could be done through a combination of frightening visuals & sounds and mechanics that would feature build-ups that give the feel of echoes growing closer and faster with every second or unnerving suspense.