During the long era when Doctor Who was off the air, the show was kept alive partly by books — and partly by audio adventures, most of them released by Big Finish. At this point, though, there are hundreds of them out there. So which ones are absolutely essential?
I'll be honest — I've listened to the Cybermen story "Real Time" because it was animated for the BBC website several years ago. I've also listened to the Cybermen origin story "Spare Parts." And I've also listened to some of the other BBC radio/audio productions, including "Slipback," "Paradise of Death," "Death Comes to Time," "Scream of the Shalka," and "Shada."
But I'm not terribly steeped in the Big Finish storylines. Which ones should I go out of my way to listen to? Which episodes would you recommend to casual fans of the series, in general?