The plot is messed up but I guess you could summarise it as masked man seeks to bring down the UKs (now totalitarian...in the future) government by a series of "terrorist acts".
The film follows Natalie Portman as her path crosses that of V and ends up getting sucked into her world. It follows V's attempt at bringing down the government and a detectives attempt to find out how V is and then.... exactly what the government has been up to.
There are spectacular special affects (non of it looks computer-y...thank god). There is plenty of action and violence, the scenes where V takes on several government policemen is miles better than the computerised fight scenes in the last 2 matrix movies (this is from the same brothers that brought us the matrix trilogy).
I thought it was excellent, it was enjoyable and much of the time fast paced, and I think it had a lot to say. I felt inspired after the film, and it made many comments on how dangerous a government can become - especially when they start taking away peoples rights.
The only criticism is that it is very long, and slows down in the middle...once I'd accepted that there was going to be loads left I regrouped and got back into it. The second half is also excellent and builds up to a climatic finish.