This scene particularly I thought was very descriptive:
The whole thing.
Light sure is displaying some lunatic god complexes there. "You're in my way, so die because I can!"
...Yet, look at L...
L has no problem sacrificing someone, even if it was a criminal. He's a hypocrite. He killed someone, he put them on the chair knowing they might die, just to serve his purpose. Yet he hunts Kira for the same reason.
My particularly favorite part, watch around 4:48 to 4:57.
"I.AM.JUSTICE!"
Both of them say it. Both of them see themselves as some nearly divine personification of justice.
They both have very shaky morals. Light will kill people who stand on the way of his vision, yet L will give away precious details, like letting Kira know he knows, details which would have made his capture a LOT easier... Just to egg him on. Just to taunt him. It's personal. It's not a service for him, it's a hunt.