It seems like it's taking a page (heh) from the Japanese drama that came out like 2 years ago.
Light doesn't really start off as Kira. He's sort of bitch made and dumb until the ending, where he seems to fully embrace the role.
It's interesting that both L and Light are alive though. They were definitely planning for a sequel. I hope they get it, if only so I can see how it goes down.
And yeah, Mia was definitely the "true" villain in this adaptation.
It's heavily implied L writes down Light's name at the end. When Ryuk appears at the end and says "you humans are so interesting" Light looks terrified