4/5. A bit disappointing. This one was too rushed, and should've been a 2 parter. If this was a 4 part story in the classic series, we got to see part 1 and 4, but not the middle. It was interesting in some ways but it also was a lot of plot through exposition. And, if you think about it, all the action happens off screen (in the Doctor's timeline).
Guess the rumors were right about Hurt appearing at the end as a forgotten "Doctor". Although, the Doctor didn't forget that incarnation, just kept him a secret.
I enjoyed seeing the First Doctor and Susan stealing the TARDIS, but that really should've been a whole story by itself!!