Light's a DBAG. (Spoilers, though all of these posts kind of are)
That book corrupted Light. It was portrayed as intoxicating, evidenced by his transformation after his first two kills and his night and day transformation after regaining possession of the Death Note.
He wasn't a hero of any sort. He was an awesome serial killer that rattled the entire world without giving up half his life (in retrospect, he might have lived longer if he had, LULZ). Killing people is wrong, trials exist for a reason. The guy didn't do research past watching news reports for suspects and then killing them. No trial, no nothing. I mean he even went to the internet for some of this stuff. How reliable is that? Justice cannot be carried out without due process to ensure innocents aren't killed.
L was a dbag too, for going Guantanamo on them. But in the end L was better. He was prepared to die and had set up his successors in that event. I'd venture to say he purposely didn't name a successor. His death wasn't shocking in that he often mentioned he could die. His demeanor seemed like he knew it was coming. If someone like L thinks he's going to die, he sets up things to be ready and picks a successor. But he didn't. He wanted both M and N ready to go, squabble and bring him down together. So they did.
On a side note: wtf was up with LMN's eyes. Coffee overuse?