Instead of an alternate dimension where Cybermen are shown to have an alternate origin, the Fifth Doctor and Nyssa go straight past the pointless work around and travel to witness the origins of the same Cybermen we'd seen all along on the series. Also, instead of alternate timeline versions of characters important to the main cast, we're introduced to new characters who are developed early on quite enough for it to be much more horrifying when they're "upgraded".
Writer Marc Platt, who wrote Ghost Light, one of the best Seventh Doctor television stories, appreciates that the Cyberman are much scarier with the cloth masks instead of the metal or plastic ones. That vulnerability, that sense of walking, eternal surgery patients, is so much eerier than the big toy case. It's not unlike the problem with the Green Goblin in the first Sam Raimi Spider-Man movie.
Spare Parts features Nyssa (Sarah Sutton) as the Doctor's companion and once again provides opportunity to explore her character far more than any of her television episodes did.
Arguments between council members and crude versions of Cybermen and a busybody official (Pamela Binns) who comes off like a Catholic school nun instructor are all wonderfully grey. Unusually for Doctor Who, no one of them feels simply evil, each one has a point of view on what's best for humanity, even the Cybermen. Really good stuff.
Twitter Sonnet #721
The pretzels of Hell reach through thick glasses.
A pale pancreas recreates the heart.
Sharpened exposition thought of asses.
Bardot's contempt traces the moonless art.
White raindrop slashes separate the ink.
Promotional moth men think of butter.
Nineteen eighties sidewalk art stains the sink.
T-shirts clog all the light in the shutter.
All crude cyborgs know that nylon beats steel.
Gold arrowheads against blue sky remain.
All plastic coils one day become real.
Sturdy pins traced a good mountain's refrain.
Permanent pachyderm decimals mate.
Extended noses need never to wait.