I must admit, when I first saw this story on the night of broadcast I was somewhat underwhelmed by it.
Reading all these teases of familiar names returning had been throwing petrol on the flames of my expectations, so the serviceable plot - a truly professional job of craftsmanship, written under the gun - by Terrance Dicks seemed a bit unspectacular, even at the time.
And I remember being particularly disappointed at Rassilon being depicted in the way he was.
Now, of course, I can look back at it and feel sad at so many faces that have gone to that great Tardis in the sky, so for that reason alone, this story is precious and, given the pressures of television production in those days and the scheduling headaches that had to be overcome (including Tom perhaps spitefully throwing a late in the day spanner in the works, perhaps as revenge against JNT) the fact that it exists at all is somewhat miraculous.
Respect to Richard Hurndall too, who created a First Doctor, who wasn't Hartnell in any way, but somehow worked, I am sure that he would have done HURNDALL DOCTOR Big Finish's had he lived long enough.
I never cease to be impressed by the fact that JNT directed the Rassilon Robot sequence. He is clearly one of the best directors that WHO never had. Perhaps he should have done a full story and shown the others how it should have been done? That sequence is, I think, the best thing in the show. This amazingly shot scene is always overlooked when people who worked with him are doing down JNT and his understanding of what made for good DOCTOR WHO.
So, imo, overall this tale is not brilliant, but perfectly okay for what it was.