It's been commented on before, but the opening moments of The Keeper of Traken really do feel more like a fairy tale than like what we've come to expect from the show. The sudden intrusion of the Keeper (played by Denis Carey, allegedly as a sort of apology for Shada not going through), and his recounting of previous events on Traken, is played more like a gentle narrator than an unwelcome presence, and even the Doctor treats him deferentially.
But what's perhaps more impressive is that this fairy tale feeling persists throughout these first two episodes. The deal that Kassia has seemingly made with the Melkur is that of an innocent corrupted by evil, rather than anything more pragmatic, and the whole meeting of the Consuls feels pleasantly at a distance from reality. This is not the same style of writing that we had in Warriors' Gate, but here it works. This is the story of how corruption came to the perfect world of Traken (where "the atmosphere there was so full of goodness that evil just shriveled up and died"), and the light fantasy feel makes this a compelling tale with a touch of inevitability about it.
The acting is generally good all around, with everyone slipping easily into this mode of storytelling -- it seems like Matthew Waterhouse gets better and better, and here he seems quite at home with Tom Baker's Doctor. Denis Carey is really good too, playing an old man who is nevertheless recognizably different from his portrayal of Professor Chronotis in Shada, and Anthony Ainley does a good job of playing a kind yet keenly intelligent man -- note the way in which he's constantly watching everyone around him, and the way he lights up when he learns that the Doctor is a scientist. Oh, and look; John Woodnutt is in this too, being as good as ever. I'd forgotten that. Sheila Ruskin is somewhat less successful as Kassia, but really, she's doing exactly what the script needs her to do, so she can't really be faulted for that. And it's not exactly a performance, but the Melkur is a gorgeous piece of design, isn't it?
And lest you think that Christopher H. Bidmead has relinquished his "more science less fantasy" position, we find that there is in fact a scientific underpinning to the goings-on on Traken -- Tremas is unabashedly a scientist, and we learn that all the magical things we've seen are the result of a piece of bio-mechanical engineering called the Source. It's a bit more uneasy a balance than in, say, State of Decay, but it still just about works. The fantasy doesn't end up overwhelming the science, but neither does the science overwhelm the fantasy, and that's a good thing.
Plus it gives that second cliffhanger ("It is done, Melkur." "Oh no, Kassia. It is only beginning") an additional edge, as it reenforces the feeling of inevitability, of a fairy tale land's downfall thanks to evil. It will be interesting to see if the next two episodes can maintain that feel.