You know, I remeraber when I first started watching Death Note, I was kind of surprised by how quickly they revealed Ryuk and the explanation of where the death note came from. I mean, most American TV series would have dragged that out. I mean, it took Lost about 3 seasons to explain any of the supernatural occurrences. Losing Ryuk would actually make the death note a little more mysterious. Ryuk might be better saved for the sequel. Besides, the comedy could easily be screwed up in a live action movie.
This is only the first movie, though. Why go all out like that when you can save some for the sequel?
The anime puts a lot of the blame on the death note, too. Light's father constantly tells Light that having the ability to kill anyone at will would be a curse that would destroy one's soul. At the beginning of the series, Light seems to be a rather normal teenager. If he didn't find the death note, he probably would have lived a normal, happy life and done a lot of good for the world. To be honest, I thought that Light went crazy a little too early in the anime. I would rather see a gradual change in Light's personality. Like, in the first movie he's just an avenger, but by the second movie he's starting to go over the edge, and by the third he's completely insane.