It all looks great. We're planted on this space ship with the Doctor, Nyssa, Tegan and Adric, and they explore a ship very slowly. Then they meet some people and, uh, then some more people. Series 18 made it very clear that we would have to sit through 25 minutes of storyline before any action happened, and I was fine with that. I'd got used to 25 minute of character introduction and scene setting, and grown to like it. The problem is that, well, about half way through the third part of this story I realised if there WAS going to be any action, it wasn't going to last very long. I remember saying to my friend "This is like the Doctor Who equivalent to Deep Space Nine: Very little happening in the far future."
Christopher H Bidmead's influence is still visible; problems are solved inventively and scientific ideas are thrown about unnecessarily (but certainly not as interestingly as during Bidmead's own scripts). I wouldn't have minded sitting through parts 1-3 if part 4 was somehow climatic, exciting and a great payoff, but you never get the sense of urgency and excitement you got from the classic stories.
It's a shame, as the central idea is an intriguing one but the execution leaves a lot to be desired.