Three out of five. Didn't really live up to its potential, and the guest actors couldn't act their ways out of a real police box. The setup seems very contrived (salvage ship beats up star-powered time/space machine). Might have worked if the TARDIS had set the whole thing up to get Clara into that room with the book, but the reset button would seem to have negated that (although it occurs to me that the salvage crew seemed to have an inkling of memory of events that were deleted and wouldn't have happened yet anyway, so maybe Clara the time-traveller remembers the incident with the book in some way).
I would have liked an old console room or two. Surely the console replica from An Adventure In Space And Time
could have been utilised, even if against a CGI background. It would have made more sense than that "echo room" stuff.
Anyway, nice to see the Eye Of Harmony referenced and explained a bit. (As suspected, the term appears to be a religious or quasi-religious name for a particular state of a former star rather than a unique object, though I had imagined that the term referred to a singularity. Still, a star on the knife-edge of collapse is a pretty good solution.)
Can we take from this that the Doctor's original name is relatively short and not absurd? That was the impression that I got. Clara's reading of the book immediately put me in mind of a scene from the very first episode, where Susan opens a book that she's been given/lent and almost instantly notices a factual error. Maybe a homage, maybe a hint, maybe nothing at all. Also, perhaps I missed something, but I'm wondering how she knew that the passage must specifically refer to the Doctor. In any case, the fact that there was a reference to the Doctor's original name suggests that the title of the season finale refers to exactly that.