Nocturne is a great champion and a lot of fun. There's very little to not like about Noc...he suffers from one major problem and that's his Ult. His Ult's awesome...it's also on one of the longest cooldowns imaginable. Playing against him...remember that. When he ults...he's not going to be able to Ult again for a long time early on. It's a 3 minute cooldown until level 11 and almost 2 and a half minutes until level 16.
He has a spell shield..so keep that in mind...do not blow something important on him if he has his spell shield up or if it's not on cooldown. He can chase like it's nobody's business if you run in a line because he has increased movement speed while he's on his dusk trail...so if he casts Duskbringer...immediately change directions to make sure he doesn't get the speed buff while continuing on a straight line.