Spoilers for the ending. Read at your own risk.
He had to admit, he felt a little bad.
And that made him laugh all the harder.
Why not? The whole situation was freaking hilarious. Who ever heard of a shinigami feeling remorse for what it was born to do? The humor of this was not lost on Ryuk, who never begrudged himself a good laugh, even if it was at his own expense
The shinigami watched the boy twisting, dying at his feet, and idly wondered if he had taken the right course of action. Not because he thought killing him was wrong or immoral. No, it was because this boy, Light, had provided him with entertainment for all these years. Though years passed like hours for him, he couldn't remember a time when he had been so engrossed in anything or anyone for any extended amount of time.
The truth was that he would rather miss this intelligent little human, whose eyes were wild as he clutched his chest. Life would definitely be duller from now on. He highly doubted that there would ever be another human like this one. Light was a shinigami born into the wrong body.
"I don't want to die!" Cried the boy who wanted to be a god, and Ryuk ached for him, ached with the laughter rumbling in his lungs.
But it was over all too soon. Those eyes, which were once alive and dancing with secrets, intelligence just beneath the surface, were staring lifelessly ahead.
Ryuk flew home that night. The human that had hunted Kira had burned the notebooks, so he had no reason to remain here any longer. As he took one last look at the human world he had come to know so well, he pondered to himself.
Surely Light truly had been a real god, because he was the only one who had ever made him feel a true emotion.