I think the second half of the show makes it all the more compelling of a series to me. While I think having the whole series be L vs Light, and having one win at the very end would certainly still be compelling, it felt kind of refreshing to have the story stretch out beyond the initial conflict. We get to see who Light is when he actually HAS this power he's been trying to gather together. We see how he grows, and also degrades, as a person. And we get a pretty interesting reversal as instead of a major police task-force with government backing facing a single rogue vigilante, we have two small groups, who by the end of the series have no government backing or are just straight up criminals, facing someone that most would consider the de-facto head of the world by that time.
I agree that Near and Mello don't quite reach L's status, but I found the twist and second half to be super refreshing for a story that, under a more traditional setup, would have ended far earlier and never explored all that.
