I read "The Trial", which is an adaptation of Kafka and "I am Legend" which is (I think) not originally a graphic novel, but a regular novel, then a movie, then a graphic novel. I picked up the trial because I thought it looked interesting. I picked up I am Legend because PB and I saw the movie and I remember him telling me how different the book was than the movie.
At any rate, I did like both of them OK. I wasn't blown away, but I think it was because I was having a hard time processing words and images simultaneously. You would think it would be easier, but I found myself so drawn to the words that I kind of skipped over the images most of the time. I think that a lot of the story in the Trial was in the pictures so I think I missed out a lot there.
I am definitely going to try The Watchmen as well - I forgot to mention that reading about that movie is what inspired me to check out graphic novels in the first place.