Old Tom Morris said:
I admit I was hoping she'd burn it all and am fairly satisfied with the end result. And if you step back, you can understand a lot of the reasons of why she's gone the way she did. I get the motivations - playing nice burned her in Essos, everyone in her life has betrayed her, fear is how she sees her way to ruling. But they needed to show us a little more capability of cruelty or madness from her leading up.
That's exactly the issue though. This episode was awesome in the "holy ****" type of way, and it's a crazy ending to the story.
It may even be in line with what GRRM has planned. I'm sure there are other examples of stories where a main protagonist becomes an antagonist at the end, but they may not have been drawn out as long as this story. I have to imagine that GRRM will do it in a more gradual way though or at least do it at a point that makes sense. After the battle is won was the time, or are we supposed to think it has been her plan since maybe Missandei died? Also, I could've seen her burning the Red Keep and killing civilians in the process, but she burnt the city first.