I liked the lore side of this story, and the concepts it explored. It provides a satisfying explanation as to why Nyssa fainted her way out of "Kinda", and also expands on Traken culture and history. It also sort of paves the way for future big, evil omniscient beings to appear in Big Finish (sort of like how "Wild Blue Yonder" did in the televised series for the Pantheon, only the Great Old Ones of Big Finish are far more threatening and compelling villains than those). Stories such as "The Lovecraft Invasion", "Lurkers At Sunlight's Edge" and the 7/Elder Gods trilogy effectively all route back to events which occurred here, so on that front, this is quite an important, root-level Big Finish story.
However, in terms of the plot itself, I found it to be quite bare and generic. The Great Old One in question here basically wants access to the Source of Traken to take over the universe, or something thereabouts. That's really all there is to it, but I think the continuity feats really cover up the facts of how basic this plot is. A basic plot can be good, don't get me wrong, but normally it only works for two- or three-part long stories or books under 200 pages long. This is a full, two-hour long 4-part audio adventure, so by the time I'd reached the end of Part 3, I was already just desperate to get to the end of it and had to push myself to get through Part 4 when there wasn't really anything to shake up the plot or reinvigorate it for the final half-hour.