Cersei has always been one of the best characters - nobody needs to think she's admirable to admit that. She is no one-note sadist like Ramsay, but someone far more interesting and entertaining to watch. I've even warmed to her a lot more as she's shown she learns from mistakes. After the familiar story in which someone imagines they'll be able to
use fanatics and theocrats, predictably ending up under a jackboot or at least a sandal, Cersei understood her error, learned and adapted quickly. When thwarted by the trial by combat being abolished, she changed course again and experimented with an... um... aggressive form of secularism.
I defy anyone to say that her revenge/power grab sequence in S06E10 wasn't entertaining to watch, no matter how villainous Cersei may be. I've mentioned the charisma she's been projecting in her triumph, so I won't repeat all that again.
With developments as they are, enemies closing in from all sides, it's doubtful whether Cersei's going to survive until the 8th series. So, after Roose Bolton, another of GoT's best villains will go by the wayside. The plot probably demands it. We've only got 13 episodes to go.
"Change will preserve us. It is the lifeblood of the Isles. It will move mountains! It will mount movements!" - Sheogorath