It doesn't matter if you agree or disagree with Light; it stands to reason that he was the reason we finished Death Note. His genius and cunning made him impossible to catch, and by the show's ending, the one person who could truly challenge him was gone, leaving him pretty much invincible.
Most of us had good reason to believe that Light would've reigned as Kira for the remainder of his life — but did he? What happened to Light at the end of Death Note? Did he die?
Near exposes Light's true identity as Kira in the final episode, causing Matsuda to shoot him. Ryuk, having decided that Light has lost, writes his name in his Death Note and kills him.
The ending is fairly the same in both the anime and manga, save a few details.
In the anime, Light escapes the Yellow Box after being shot and steadily makes his way to a hideout. As he limps across the street, he hallucinates his younger self walking towards him, symbolizing his regret at ever having picked up the Death Note.
Ryuk sets off on a monologue about his promise to Light (that he would be the one who claimed his life) and writes his name in his notebook. Light dies of a heart attack in the middle of a flight of stairs, and the last thing he sees is an apparition of L.
Whereas in the manga, Light calls on Ryuk to help him. He asks his Shinigami to write the names of the Task Force members in his notebook, and Ryuk agrees — except he writes Light's name instead.
Light dies 40 seconds later of a heart attack, right in front of the detectives gathered in the Yellow Box, perhaps as a form of poetic justice to the people that spent their lives trying to catch him.
In both versions, Light's death is the final act. The credits roll as we see Light's lifeless body, leaving us hollow and in temporary shock.
However, the Netflix adaptation takes this beautifully crafted ending and throws it in the bin, effectively ruining the series.
The entire film feels like an insult to the original series, but the ending is worse.
After an argument between Light and Mia (Misa's counterpart for the films), Mia plummets to her death from the Ferris Wheel. Light survives the crash and is rushed to the hospital, where he tells his dad his reasons for using the Death Note. The movie ends with the Death Note in L's possession, who we assume writes Light's name in it.
The movie director, Adam Wingard, was confident that the Netflix adaptation would score a few more films, prompting him to end the first one at a cliffhanger.
But that never happened, so we have no way of knowing if the ending he planned was going to stick to the source.
Given the complete disregard for the manga (or logic, for that matter) in the first film, the bet is that he had no intention of doing Tsugumi Ohba's writing justice. It's a blessing that the movies weren't allowed to progress.
Ryuk was never on Light's side. All he cared about was being entertained, and as soon as Light's ruse was exposed, Ryuk decided that waiting for Light to die a natural death would be boring, so he killed him.
The agreement between the Shinigami who drops the Death Note and the first human who picks it up is that when the time comes, the Shinigami would be the one who takes the human's life. The Shinigami will also be required to stay with the human until they die, and only after witnessing their death will the Shinigami be free.
Ryuk knew that even if Light managed to survive the gunshots, the police would throw him in jail on a life sentence. The idea of sticking around Light for so long bored him, which is why he ended things when he could.
It's the same story in the manga. Ryuk knew that Light must be truly desperate to beg him for help and decided that he would no longer be entertaining.
Some people also believe that Ryuk killed Light because he didn't want him to suffer in jail. It's nice to think that's true, but Ryuk in canon harbored zero attachments to Light. If he did, he would've killed the SPK and Task Force when Light asked him to.
Light Yagami went to neither heaven nor hell. Tsugumi Ohba confirmed that the afterlife doesn't exist in the Death Note universe and that all those that die go to "Mu" (nothingness).
Light figured as much after Ryuk said he wouldn't go to hell or heaven.
Ryuk was surprised by Light's perceptiveness here. He agreed and told him that the place humans go to after they die wasn't decided by a God and that death was equal for all human beings.
Near burned Mikami and Light's Death Notes, and as told in chapter 107 of the manga, there were no more Death Notes in human possession. In the short stories that followed, two more humans got their hands on the Death Note.
The first one was dubbed C-Kira (Cheap Kira) by Near. This Kira killed hospitalized older people (his motivations were unclear).
When Near announced that he had no interest in the case, since he'd deduced the new Kira was a cheap wanna-be copy of the original one, the C-Kira wrote his own name in the notebook and died. The Death Note then made its way back to the Shinigami Realm.
The second time was when Ryuk got bored again and decided he wanted someone to follow in Light's footsteps. He picked Minoru Tanaka, a high-scoring middle-schooler, and presented him with the notebook, but the boy refused and asked him to come back in two years.
Minoru told Ryuk that he planned on auctioning the Death Note online, and as baffling as it sounds, the kid managed to make it work. Intrigued, Ryuk did as he was asked and returned to him two years later. He sold the book to the President of the United States and managed to remain untraceable by Near, who eventually admitted defeat.