If this were any other series, I'd be concerned about this new purpose because it has an eventual end-point. But I know this is one show that will never run out of ideas, so, why worry?
I liked the three doctors, although that's probably the end of John Hurt's stint. I especially liked seeing Tom Baker show up at the end. He's still my fave. An Adventure in Time and Space was disappointing; it was mostly homage to William Hartnell. I wanted to see more of the "how" behind the origins, such as the casual way the interior of the Tardis was "designed", if you can call it that. How did they come up with the idea of the Daleks in the first place? And that music -- all we were shown was a hand jotting down notes on staff paper. Who invented the sonic screwdriver? Or the dog robot? That's the kind of thing I wanted to see.