I always feel a bit sorry for the two other, non-speaking, Terileptils, who seem to be yes men to the their leader (the Terileptils are one of those races that don't have names for each other), and are rather timid creatures themselves, unable to use firearms and rubbish in a fight.
Witness the climactic fight in Episode Four where one of them tries to attack Richard Mace, who is holding a loaded gun, but fails miserably. Mace then swings round, takes aim at the poor, pathetic creature, and fires on the helpless fellow. If the Terileptil could have spoken, he would have been saying "Sorry! Sorry! Sorry!" in the seconds before Mace killed him at point blank range. Richard Mace, you have no soul.
The Visitation works reasonably well, although this is based mostly on the novelty its historical setting (this story being the first historical since 1977's Horror of Fang Rock). However, there is a distinct lack of characters throughout all four episodes. Apart from the odd villager, and the family at the beginning of Episode One who meet their end after their opening scene, there are only two major speaking roles in this story - Richard Mace and the Terileptil leader. The lack of characters leads to a lack of dramatic subplots, with only the comparatively trivial exploits of the various companions serving to break up the main plot. Witness the drawn out business of Nyssa creating the sonic booster to deal with the android. It not only gives Nyssa something to do for most of episodes 2-4, but it shoehorns a long, almost superfluous subplot into the action when it didn't necessarily need it.
The Visitation is an enjoyable enough watch, though, and features some great Ealing film footage in Episode Four. Not the last we'd hear from one Eric Saward, either...