I don't care much about the allegory aspect of V For Vendetta, what hated about the film is how black and white they made everything. God, they even had the Head look visually identical to Hilter. The novel actually portrayed the government as people who, while not necessarily good, felt what they did was for the good intention, and V could be just as insane and crazy as he could be heroic. It took a very complicated story and made it overly simple. Maybe that's better for some, but definitely not for me.
But I disagree that it just ended, but we've discussed this before. All the major plot points were resolved by the end of the story, we just never got to see the fallout from it. Intention ambiguity to how people would react to the new situation.