Inspired by Philip Pullman’s The Amber Spyglass, and wanting to provide a cataclysmic event that would keep the Doctor and Rose apart forever, Russell T Davies decided to leave Rose trapped in a parallel universe that the Doctor could never revisit.
Doomsday, then, saw the culmination of a two-year plot arc, and it is heartbreaking. All of us in the audience had watched these two characters travel together, and grow together, ever since the show returned; it was with the Tenth Doctor that we really saw the depth of feeling these two characters had for each other. Notably, however, their feelings had never really been expressed to one another on screen before; though we all talk about the epic love story between the Doctor and Rose, it’s actually far subtler and much more understated than that.
Expanding somewhat on my recent review, I’ve written a Yahoo article about Doomsday, talking about the Doctor and Rose’s relationship, the bond the two shared, and that final scene where they’re ripped apart forever. It’s great stuff, really; rewatching these episodes, I was quite keenly reminded of just how much I love Russell T Davies’ Doctor Who work.