I have Nocturne, but I don't like him. I could just be bad, but these are my opinions.
The main thing about him is that he COMPLETELY blows up in team fights early game. Build offense first, enemy team switches focus and he dies in a second, even with correctly used spell shield. Builds defense first, does **** for damage on his Q cooldown (and that is not even completely reliable). I just don't like him because he has no presence until he builds offense.
He has decent clear times, and pre-6 his ganks are very good, and better at 6. But I feel like unless he gets a few early kills, he has trouble catching up in gold to survive in teamfights. He requires an early Aegis or Frozen Mallet along with a Bloodthirster or something for damage.