Naturally the inclination is to disbelieve in the power of the comic-book format to tell a socially relevant and emotionally powerful story, and most of the genre is cluttered with nihilistic power fantasies these days. But this is a brilliant exception, and that can be attributed to Alan Moore's powers as a writer.
You can read the rest of the reviews and find a lot of spoiling detail about the narrative, but the best aspect lies in an attention to the small and overlooked people whose feelings Alan Moore makes very much a part of the entirety. In what I think is the best moment of all, one of the characters imprisoned by the secret police of the English totalitarian state reads and envisions the final thoughts of a dead lesbian, written on toilet paper for some future prisoner to draw hope from. I felt an almost tearful admiration for the sort of bravery and faith in oneself that this prisoner discovers, and a more conscious recognition that Alan Moore is one of the best ever to write for the medium.
It's indisputably good, but it thumps the pulpit of the author's choosing - all government steals self-determination and liberty from its subjects, civilization and barbarism are close neighbors, the masses remain wilfully ignorant of the big picture to focus on television fantasies. It's a deliberately simple portrait of a dystopia, and its questions demand thought from their readers. You might love this as much as I do, but rest assured it won't be because of simplicity or polite avoidance of libertarian doctrine.