Writing dialogue for a comic book, no matter what genre, is absolutely frustrating for the novelist. I believe perhaps it maybe easier for me, seeing that I write horror and dark fantasy. There's some, not a lot, but some practice with condensing your verbiage.
What has to happen when writing for comics is.....each word must be carefully weighted, petted, cooed over and dissected from each angle before you use it. Each word has to convey the mood, the meaning and the overall theme.
When writing short fiction or a novel you can use pages or paragraphs to covey these messages. In comics you MAY, just MAY, get to use four words.
Most of your story and the lives of your characters should be see by the reader, like a snapshot in one space of time. most of your writing conveys limited directions to your artist on how you want the panels to look and the overall feel of the entire story.
My job as the writer is to condense everything the characters need to say and the actions and interactions into twenty-two too thirty -four pages of awesomeness. Within these pages I've got my theme, the plot, the background of my characters, their motivations, and the creation of a story that makes you want to give a fuck about why they are doing what they do.
The time I spend on each section of dialogue is MONUMENTAL to what I used to do when pumping out short fiction or working on a novel.
I can tell you this type of writing makes you smarter, more creative, concise and well planned with the journey you commit to taking. You come to understand that empires rise and fall from the whisper or shout of just one word.