Comic book movies. Either they are based on pretty bad comics, and in that case their origins can be ignored, or (far more rarely) they are based on good comics, which makes one dread them in the same way one dreads movies based on good novels. No matter how good they are, they risk somehow betraying their source material. Once in a while, you get lucky. Ghost World is an OK movie based on a great comics. The Big Sleep is an excellent movie based on an excellent book. But double whammies like this are rare.
I loved the Posey Simmonds graphic novel, and this movie adaptation by Stephen Frears looks quite good too.