It's dark, not over-lit as colour might well have been, so the black and white serves well to enhance the atmosphere. There's a bit of over-acting from time to time, but generally the script is taut and well observed and the actors deliver it with calm assurance. They are utterly convincing.
The Colonel-to-become-Brigadier is a strong and assured character from the start, military in his outlook, although quite receptive to new ideas in some ways. Nicholas Courtney is excellent in this. Patrick Troughton is delightful, quietly turning events and manipulating the humans into excelling themselves. This Doctor is a catalyst. Frazer Hines delivers a convincingly well meaning but uninformed Jamie. Deborah Watling is the screaming young female, but she shows great bravery whilst racked by fear.
All in all, this well lives up to its memory and its reputation. It follows straight on from The Enemy of the World, also recently found. The reproduction and sound quality are also first class, so a great restoration has been done.