Doctor Who jumps into the world of space ships and moon bases full force for the first time since 1973's Frontier in Space. It's a welcome sight in some ways, but the results are mixed. There's a model sequence featuring a shuttle landing and being transported deep inside the base on Titan that looks quite good, but other shots never let you think that the spaceships are anything else than lightweight models on strings.
The new/old TARDIS set makes its first appearance in a while, too. Replacing the wood panel set of Season 14, this version would remain relatively constant for the duration of the classic series. Showcasing it here, though, means that there's a few scenes featuring Leela hand writing and others featuring general silliness that keep The Doctor from entering the story. There's also a lighter feel to things. This is Graham Williams's first story made as producer, and the grim aspects of his predecessor's time on the show are a distant memory already.
Along with some dodgy makeup and some even dodgier dialogue, The Invisible Enemy does not start out as well as one would hope, despite the best efforts of the ever reliable Michael Sheard.