I just don't care for this one very much. After a pretty strong run of introductory episodes, this one, in my opinion, really doesn't stand the test of time very well. I find the plot terribly boring, the aliens quite silly, and the quality varies quite heavily between episodes. There are some decent moments of tension I found early on but after a while it feels like the story really has nowhere to go, at least not until the Doctor gets to have some fun playing lawyer (probably my favourite bit in the whole storyline). Keys of Marinus drifts too heavily towards the standard sci-fi of its era, in my opinion, falling far short of the more brilliant moments in Doctor Who history. Really only recommended for those seeking to truly complete their Doctor Who experience. Their are far better stories from this era and worse, this can give you the wrong impression of what that era can be like, with a heavy focus on Ian while characters like Susan are left to flounder. Still, the story does have some decent moments with the Doctor and even the companions, and I don't hate it, either. You could do better, but to be clear, you could also do a lot worse.