It's often very hard to pull off getting into the Doctor's head like this - he's the Doctor, but you've done it so very well here, it's brilliant. I only know the Sabbath arc very vaguely but it didn't matter: it's a wonderful look at the Doctor, and at Eight in particular.
Very well done
Wow, I take it there's a lot I've missed by not reading the books... but it doesn't matter, this is a very well-written character study. And I LOL'd at "No, I’m not saying that I want to turn to the Dark Side… You were the one that made me watch that film, stop complaining. Where was I? Oh, yes."