While I liked this, it was probably the weakest of the run (4.5/5 instead of 5/5)

These are not big issues, but they're annoying, so I am going to spend a lot of time on them:

Weirdly, I think the weakest parts were the bits with the Doctor. Obviously, Tom Baker's performance was great, but it felt like whenever he's around, the story's priorities changed. The writer stops caring about telling the story he's been telling for the past 2 hours, and is just writing fun lines for the human man Tom Baker to say. There's this weird thing that expanded universe writers will do whenever they're making more than a passing reference to a tv story, where they'll have the doctor stop and reminisce and give a full summary of the story, regardless of plot relevence. The other characters don't care. Most of the audience of a Big Finish story featuring the 4th Doctor and Morbius have already seen The Brain of Morbius and know all this, and the rest don't care. It feels like the only reason it's there is because fans get a nostalgia hit hearing Tom Baker say Solon

This kind of thing does have an impact on the story itself. I'm still not totally clear on why the Horn of Rassilon summons the Doctor, rather than Rassilon, but hey, we get that awkward conversation where two people who've never met the doctor before have to try and naturalistically prompt him to explain where he is in relation to his TV timeline

Again, these are minor issues, and most of the story is great, I just can't shake the feeling that Tim Foley got a little distracted by continuity once the doctor showed up, and the story suffers slightly for it