Third rewatch and still amazed by this masterpiece. "Heaven Sent” is the very embodiment of the word "perfect". Each viewing makes the episode even better, noticing details I hadn't noticed before. I'm not going to go back over the Doctor's writing, which is immense, and he's THE best character working of all time, I'm not open to debate. Everything is mastered, whether it's the direction, the writing, the concept, the acting (I can't repeat it enough, but with Cranston in Ozymendias, Capaldi delivered the best acting performance in an episode), the monologues, the quotes, the photography, the editing... All the categories are combined to make the ultimate episode of Doctor Who and of television. I honestly don't know what else to say. I'm still in awe on every rewatch. This is and will remain for a long time my second favorite episode of all time (only twice upon a time is better).