Although both graphic novel and film end with the masses casting off the authority of the Party and explosions (although the chronology and exact content of these events do differ), this difference is particularly salient when one considers the point of the Guy Fawkes mask. In the graphic novel, the mask allowed V to remain anonymous, allowed him to represent an idea.
This idea is not extended to the whole of society - who V is is not experienced by the whole of society. Although V intends for there one day to be a land of Do-As-You-Please, he understands that the masses, freed from totalitarianism, are constructing first the land of Take-What-You-Want. Evey manages to reach the place of understanding that V inhabits only through intense physical and psychological trauma - V's understanding is not something that people will achieve with the simple toppling of a government.
The film presents a much different view of the mask and of society itself. In the film, anonymity is key to rebellion - the mask that hides the individual from authority is what allows a rebellion to take root and flourish. And as Evey notes at the end of the film, V was "all of us" - not just an idea, but an idea that all can easily understand and embrace as long as one has, say, a Guy Fawkes mask. But this is another key point: in the film, the masses rose up because of their new-found anonymity. In the graphic novel, the state was cut off from being able to observe the masses constantly, but no one was anonymous. Everyone saw everyone else's face - except the government.
This is not intended to be a simple recap, but a positioning of a problem. The film and the graphic novel offer very different prescriptions (this is perhaps exacerbated by the fact that the graphic novel takes time to note that the immediate aftermath of V's death and the rousing of the rabble does not create the land that V would want to live in, only the precursor to that land) - they also offer very different ideas of the lengths to which the crowd will go and what the crowd can achieve (V is fundamentally different from society in the graphic novel - his thought process is described as inhuman by a member of the Party establishment multiple times).
Considering how different the two pieces are from each other, what can we take away from that? It is obvious that the message of the film has a more lasting resonance to more people - the adoption of the Guy Fawkes mask en masse by Anonymous is obviously lifted from the film, not from the novel. Does that matter? Alan Moore himself firmly believes that the two pieces speak about very different things, with very different motivations and actors (totalitarianism vs anarchy and modern-era conservatism vs populism) - does this matter? If these two works are telling their audience how to live their lives, or the choices available to them (if they are asking their audience to do something instead of just attempting to entertain), then how do we reconcile the more sober reflections of the graphic novel with the widespread popularity of the film?