I was less happy about the final part, Sepulchre, which not only relies rather heavily on reference back to the previous Hornet's Nest series, but also demands little of the actors, Tom Baker in particular doing much more Little Britain than Doctor Who; and the conclusion is very far from conclusive.
So in the end my recommendation is that this series is for completists only; the first and fourth parts are the best, the third and fifth least satisfactory.