I still personally think it's weird that Sparda could live in peace (supposedly) for 2000 years in the human world and NOT have a whole bunch of kids. That sure seems like a long time to only have 1 wife and two kids.
Anyway, on topic... I feel that Nero is just Nero, as someone else said. He looks a lot like Dante because the designers didn't want people to not be able to identify with Nero's looks. If he looks like Dante, trash talks like Dante, and kicks just as much butt, Fans of the series will feel right at home with Nero.
But as another poster said, if they didn't include Dante, it wouldn't be DMC, so they threw him in there.
As far as Nero's arm and power are concerned, I think it's Vergil's spirit....
-The Demon that shadows over Nero looks like a remade version of vergil, with the sheathe attached to his arm and everything. (this point holds water, cuz Dante's look for the DT changes with each game too).
-"From that day forth... My arm changed... and a voice echoed... Power... Give me more power!" Vergil was very power hungry in DMC3
-If I recall, "Nelo Angelo" was mistranslated, it should've been "Nero Angelo". Could be wrong on this, but if it's true then it explains why Dante said Nero had a nice name. That or he was just being nice! =D
That's my thoughts on it!
said AzureDragon87.