I know it may be weird to say, but in all actuality Ryuk is my favorite character in both the manga and the anime. Light is a little to insane for me to like him and his god complex is a little ridiculous. L I like as a character, but I think there could be more character development for him, he is kind of personality-less. Ryuk on the other hand is just full of spunk and charisma. He starts this whole situation simply for the fun of it. The amusement he seems to get out of humans is like the fascination people have with car accidents. It's tragic but curiosity always gets the better of people and they can't help but stare. Ryuk is content to sit back, relax and watch this train wreck unfold before him. I can understand how he might be equated to the devil of the crossroads because he is in a way making a deal with Light to protect and use his book, especially because at the end Ryuk is the one to kill Light. So it is somewhat a selling of the soul type deal that you would make with the devil. Personally I don't see Ryuk as a devil; however, he is not the one to corrupt Light. Without his help or guidance Light begins to kill people and "purify" the world on his own. Ryuk simply drops the book to the human world, it is simply chance that Light decides to pick up the book and bring it home with him. Now had Ryuk specifically chosen Light or actually given him the book it would have been a different situation. I do think Ryuk does play an important role in the manga though.He is the reason this epic power struggle between Light and L begins. Without Ryuk's Death Note, Light would never have gained the power to start his fight against the corruption of the world and L would never be tasked with ending his "righteous" crusade. Ryuk almost becomes an innocent bystander in the manga, as he is always at the sidelines of the action. But without Ryuk the manga would not have the demonic and threatening overtones that occur throughout the book. He is the mystery and the darkness that makes this manga so incredibly compelling to read.