I did not read the novel but i totally enjoyed the show. My galfriend slept it out though!
I guess it is kinda appealing to a specific group of audience. Indeed VERY though provoking. In fact I'm now going to buy the graphic novel!!
I feel that knowledge of American and world history along the time period 1960-1980s will help understanding the movie if you're watching it without first reading the novel. I realized alot of stuff can be better understood (the ironies/what could have been/jokes about conspiracy theories etc) if you had prior knowledge of the particular bit of real history as compared to the Watchmen timeline.