It actually isn't bad. I don't think Shiv is a TERRIBLE item on Nocturne. He is actually pretty versatile. You can honestly go any combination of dps, tanky, and tanky dps. He scales very well with AD and attack speed, but IMO the best way to play him is a tanky DPS role. Depending on the rest of your team you can go as defensive as need be. I usually go:
Wriggles Mercs Mallet Bulwark Black Cleaver Randuins
Sometimes I will sub in Warmogs for one of the above items, such as if I don't need MR and someone else is building Bulwark, or if I need to go full tank mode I will get rid of Black Cleaver. I know almost everyone builds warmogs, but the mallet and randuins give you enough HP, unless like I said you need to build PURE tank.
Wriggles is good on him since he has built in attack speed. Mercs are good on any melee to reduce CC. Mallet is needed to slow people down. Bulwark is just a great item overall, even if someone else built it. Black cleaver works with his kit extremely well IMO. Randuins is very underrated, it basically makes it so that if you get attacked while sticking to a carry, you will lower their dps, as well as the active.
You can also build a variety of offensive items such as zerkers boots, bloodthirster, infinity edge ( only recommend if EXTREMELY fed for early win ). Sword of the Divine is actually VERY good on him as well. Basically you pop SOTD active and most likely something will melt. --- #1 LoL Poster NA: http://www.gamefaqs.com/boards/954437-league-of-legends/63627116