I'll always thank that 2-parter for making Silver Nemesis look like Tomb of the Cybermen in comparison.
The Cybermen have had so many godawful moments over the years, but I don't know if anything can beat the Cybercontroller falling into the exploding power planet in slow motion, screaming "NOOOOOOoooo!" and then somehow disappearing entirely ages before he reaches the flames.
Thank Rassilon we've moved on from then (*remembers Clara's slo-mo fall on Christmas*)... Fuck.