I hadn't read either comic before watching the movies.
V for Vendetta, I was watching it and it was clear that they were making a heavy-handed criticism of George W. Bush. It was so simplistic (I'm on the far-left btw) that I was offended. I looked it up online after watching the movie and found out Alan Moore had the same opinion I did, he said they made his comic into an "American Liberal fantasy".
Watchmen, I took it on its own, without reference to the comic I had not read. I liked that it was slow and philosophically deep. It had a huge amount of courage, for example it showed the superheroes committing war crimes in Vietnam, you don't expect that from an American movie, contemporary Hollywood movies mostly show Americans as being the victims of the Vietnam war. For example in Bryan Singer's Days of Future Past, Vietnam is presented as a war that victimized Americans, and nothing else.
In later years I found out that Paul Greengrass was a competitor to Zack Snyder. He wanted to do to Watchmen what was done to V for Vendetta: to make it about George W. Bush. I'm glad he didn't get the job.
I now realize that this is another avenue in which Snyder is distinct from other blockbuster directors: he actually likes and is interested in history. He's made 300, Watchmen, Sucker Punch takes place in the 1960s (and other periods), and so on. His first instinct is not to be completely ignorant of the past and to study the present in isolation of any historical context.