First, I will say that all the actors did an excellent job in their roles, especially Hugo Weaving (aka Elrond the elf aka Mr. Smith). I think it's not an easy task for any actor to endure you to the character he is portraying if you cannot see any facial expression. We weren't even able to see his eyes. Mr. Weaving had to rely on his voice and his other body language to make the character "V" come alive. Kudos to him for doing a bang up job.
Natalie Portman, well, she's a not too bad of an actress. Her London accent was a tad off, but overall a pretty good performance. I mentioned that I saw V for Vendetta to my friend N., and his first words before I could pontificate on her acting abilities is that "she's hot". Sigh. Nuff said about that.
One other actor I would like to commend is Tim Pigott-Smith who played the bad guy Creedy. I saw him as Richard Hale in North and South, and I'm continued to be amazed at how well actors can really get into their characters and make them really believable. (Richard Hale and Creedy are polar opposites in terms of characterization, so it's a real treat to see some great acting from the same actor).
The gripes I have about the movie are mainly the storyline. Dave fell asleep for the first 15-20 mins of the movie. I don't exactly blame him. Some of the dialogue was unnecessarily, like V's "V soliloquy". Another part that I didn't exactly get nor did I think was all that useful in the script was the whole interrogation scene with Natalie Portman. Sure, it explained a few more things about V and it propelled Evey (NP's character) to a certain realization, but I didn't think it was necessary. That was a good 15 mins, I think. Rather, I would have spent the time explaining how Stephen Rea's character (the chief inspector) figured out where V's hideaway was. "It's just a feeling" just doesn't cut it for me.
Rotten Tomatoes gives this move a 75% rating (ie 7.5 out of 10). I will have to say that I agree with the assessment.