Nocturne is in a spot where he really is not tank enough to dive, not burst enough to assisinate, and has long cool down with being mana hungry.
He does have one of the strongest level two hanks in the game as he can start red hit lvl 2 and imdiatly gank mid. He is good at splitting and killing split pushers.
But he is kinda like eve. Just doesn't do anything well enough to shine. He is by no means bad but he just is not that great.
He is in the best spot since his nerf back in season 3 right now. He will remain lack luster until the rework his passive or change his fear mechanics as the fact the enemy runs away from you upon fear hurts him in 7 out of 10 cases.