I've always wondered whether or not the movie adaptations of comics hire out or at least in some marginal manner, employ, the original writers and/or illustrators of the comic. Often there seems to be a love-loss between the comic and movie mediums which could be in part to a lack of reference with the comic's writer and/or illustrator. It's not because the mediums don't correlate or lack some type of equitable relation, the matter's dependent on contour.
Most comics avert from a frame-by-frame depiction while movies require just that. Say you make a movie out of a comic, but due the discrepancies of their mediums, have to place "filler" in-between spaces a comic would omit. This results in a take-away from the comic by merely adding or subtracting scenes for the movie adaptation. If a comic were stylized as a kind of hybrid between the two, I'd imagine the transference would go a ton smoother. It's just that movies have a pretty standardized formula, while comics offer a greater variety of style.
I'd have to say V for Vendetta was one of my favorites. Watchmen was over hyped in my opinion, but the story is very compelling; moreover on a convoluted end of the spectrum, that I felt mainstream movie goers had go over their heads.
P.S. I think movie writers just aren't very good, but given some of the dialogue I've read in comics, comic writers my fall under that as well. I say this well-knowing there are quality exceptions to the statement.