It's often because, by their very nature, they are designed for a completely different format.

One I forgot about, however, was 'Sin City'! I never read the original material, but I liked the film, considering what it was. It didn't have any illusions about itself and was literally a 'moving' version of a comic.

To truly make them films, however, requires something else. It's the same problem many computer game adaptations often have. 'Tomb Raider' had excellent potential, as did 'Bloodrayne', but they ended up being overly superficial. Making them into films should be a case of shifting the elements around, so that they suit reality more than they otherwise would.

In many ways, I think that certain properties should stay in the realm of CGI films. 'Tomb Raider' should have gone that way and the only interesting story in 'The Animatrix' was superbly designed for that medium, in my view.