That said, it's probably a good idea to dispense with the political stuff first since clearly more people care about that than they do about whether or not the movie's any good. It's actually in the politics that the movie is most faithful to the comic. The message is not pro-terrorist, but anti-totalitarian with a bit of "a pox on the populi" for allowing fear and the temptation of secure comfort to overwhelm the desire for liberty. In other words, it's a warning shot fired at a chickenshit populace that would allow external threats to freak them out so bad that they'd willingly submit to a regime which not only incessantly monitors, manipulates and coerces the populace, but heards blacks, Jews, Arabs, gays and anyone else deemed "dangerously different" into concentration camps for the purposes of genetic expiriementation and eventual death. If there's any pro-terrorist message it's that some acts of violence against such a state are justified. If this is a controversial statement then we ought to re-think our response to the Germans in WWII or, if current rationales are to be believed, the Iraq War. We also ought to re-think our own nation's existence; we engaged in acts of sabotage and terror and then fought a war that killed far more people than "V" does over something far less oppressive. In any event, if someone wants to dig up a piece of pop-culture that will really tick them off due to its accidental relevence to today they might try Dune instead. Even though it's 30 years older than "V", it's far more relevant to today. Jonah Goldberg or Michelle Malkin or Christopher Hitchens might even get a kick out of digging up Frank Herbert's corpse, giving it a severe beat-down and then burning it since the bastard had the unmitigated nerve to write an "objectively pro-jihadi piece of agitprop" back in 1956.
So how does the film measure up? It's a mixed-bag generally. Part of the problem is that, as Allan Moore himself has said, his books are explicitly constructed to be untranslatable to film. In the case of "V" there are several places where the script of the movie lifts directly from the book and this merely demonstrates the stilted nature of Moore's narrative style. In other places the Wachowskis have emulated Moore's style to a fault. It's obvious that the Bros. W. are dyed-in-the-wool comic geeks and have attempted to stay faithful to the style and substance of the work; but that style tends toward long-winded monolgues over subtle suggestion. We knew this from the second and third installments of "The Matrix", though, and it's far less offensive here.
Where they have taken liberties with the story it is again hit or miss. Some of the important elements of Moore's fascist dystopia are missing. The inevtible collusion between common thugs and the leadership of the state as essential to fascist success is something often left out of popular discourse on the subject, and the absence of it is something of an unforgivable oversight. The elegant "organs of state" structure of the regime is also missing. In the comic each of the essential functions of the control aparatus is anthropomorphized: visual survailence is "The Eye", audio survailence "The Ear", investigation "The Nose", propoganda "The Mouth" and enforcement "The Finger", with each section having as its minister a distinct character. Thus the sobriquet "Fingermen" for the police/enforcers makes a little more sense than in the movie, where we just hear the name. We also don't learn much about the other ministers other than Finch of the "The Nose" whereas in the comic each one was essential to the resolution of the story.
The germination of the state, however, is more successful in the movie. The Wachowskis have wisely replaced the nuclear near-miss and resulting chaos of the comic with a bio-chemical attack. This is more chilling than Moore's vision, because in the comic the "Norsefire" conglomerate siezes control, where in the movie the populace, out of fear, elects them. The modification of the "Leader" character is also effective. In the comic, he was a subdued though fanatical neurotic, whereas in the movie he's a blustering demagogue - far more appropriate. Likewise, the transformation of Lewis Prothero from the comic's "Voice of Fate" (he's meant to fool the populace into thinking his voice is that of the malevolent computer "Fate") into a Bill O'Reilleyesque yack-show pundit (who's physical likeness to Christopher Hitchens is probably unintentional but still satisfying) is incredibly effective.
While Natalie Portman gives a first-rate performance as Evey and her new backstory is superior to that of the comic, I don't like how they resolve her involvment with "V". There's an essential duality in the comic which, while explored, isn't quite as cool. I won't go further into the details because it'd be a spoiler. I will say that I liked the old ending a little better.
Another instance on improving the book is in the character of Finch, the man in charge of investigating and apprehending "V". In both the comic and the movie he is cast as the talented everyman. He's internally conflicted; he has doubts about the nature of the regime he serves, but he knows he's "gotta eat" and has a talent which allows him to do so. Through his investigations into "V" he learns more about the history and nature of the regime he serves and his doubts grow. Eventually he transforms from reluctant participant to willing outcast. In the movie, the pacing of the investigations is much improved over the comic, and one annoying scene of the comic, where Finch takes LSD in order to "get in the his(V's) head", has been removed. The investigation, instead, takes a far more natural "police procedural" course and is the better for it. Steven Rae does an excellent job through all of this, making Finch the true center of the story.
Finally there is the character of "V". Quite honestly, the Wachowskis are probably the only people who could have got this right, and if they hadn't, they should have been forbidden from making another movie. Luckily, this is where the film is most successful. They've utterly nailed the look, from the flowing black cloaks to the eerie perpetually smiling Guy Fawkes mask to the precision of the knife work. His voice is that of Agent Smith from "The Matrix", a perfect juxtaposition, and it sounds just right giving all those soliloquies about liberty, culture and vengence. They've also nailed his movements, where all you see is the flowing cloak, the face, and suddenly the results of the action.
All in all, I'd say I was pretty satisfied. I'm not sure the movie is as important as some are making it out to be, but it's about as faithful an adapdation of a great comic as is possible.