They've managed to keep much of the book's look intact, in that V's costume is consistent, Evey looks about right, the iconic imagery is there, etc. They've gone for a more futuristic look than the Neo-thirties of the book (or whatever timezone Lloyd nicked the art from), but that's fair enough - it's supposed to be in the future.
I was pleasantly surprised how much of the basic story they kept, too. The Vendetta is still there, as are most of the principal characters: Finch, Prothero, Dascombe, Creedy, and Leader Susan (although, for some reason, here he's renamed as High Chancellor Adam Sutler; the name I can understand, but why change the title?). Two of the key women get the chop, though, and here, I have to admit I can't remember their names, but they're the two that are involved with all the leading figures in the Finger/Nose/Ear, etc.
Some sensible changes, too. For example, The Voice of Fate becomes the Voice of London, and instead of being a radio broadcast, it's now a TV show, with Prothero a public celebrity. Well, TV makes more sense than radio - the cinema-goers are more likely to believe that, and Fate itself has been dropped entirely (although there are subtle hints, in that V manages to arrange wide-spread distribution somehow - see below.)
But there are bad bits, too. There are unforgivable changes to V's character, wherein he is given doubts, surprises, etc. In the book, V is always in control; while he seems to be calm in the face of surprises, later events show that those coincidences were pre-planned, and V is rarely caught off-guard. Here, Evey's entire involvement - the story of the movie - is on a whim, and thus is much of the film undermined.
And the script. I wonder: apart from the journal and Valerie's letter, were any of Moore's original words used? Instead of his multi-layered script that makes the reader think and re-think, everything is translated into mostly-plain English (we still get the Shakespeare quotes) so that we get the sledge-hammer hint before events move on.
The opening's different. Evey isn't attempting to become a prostitute in order to get money, so we don't think she's weak, in that way. Evey receives no training from V, so the ending has to be different. V gets involved with deals with Creedy to eliminate Susan - I mean Sutler - presumably because they've lost the necessary characters from the book - and none of that fits with the character. V just isn't that stupid. I don't care if it gives us a chance to have another matrixy fight scene. Mind you, it does move Finch's final choices into the core of the story, rather than being on the edge.
The delivery is of masks instead of leaflets. This replaces the anarchy period, while Fate is blacked out. That's fair enough.
The language is very much toned down. It's interesting how we see Evey's transformation practically unchanged, and yet all the pejoritive hate-terms have been wiped from everyone's vocabulary.
There's some new stuff thrown in: St. Mary's. Three Waters. The original programme being about producing chemical weapons that were then tested on the population, with almost 100,000 people dying. I see no reason for this inclusion, nor why the concentration camps that systematically wiped out much of the population of England are only hinted at. I mean, I don't see why one's a more valid reason for bringing down a government than the other.
Overall, I'd say this is much, much better than I'd feared, and it retains enough of the original to be surprisingly bold, as a statement, given the current climate. But Moore's book is some much more, and so much better. I strongly recommend anyone who hasn't read the original to do so - twice, in succession.