Well according to pretty much anyone I've talked to the story is pretty much non-existant and is just their to give some form of sense to random sadistic violence.
Eh, depends how you look at it. I couldn't bear to watch the violence if it wasn't for the story really; I just happen to love John, Eric, Rigg, Straum, etc, etc as characters. I recommend you atleast watch III and IV before seeing V, as it will make the movie alot better for you.
As for V, I cannot wait to actually watch it. I read the ending unfortunatly... quite.. disturbing for me atleast. (Fave character dies.) But I plan on seeing it anyways.