i think RTD can certainly write sci-fi -- gridlock and midnight are two of my favourite episodes of doctor who, and although dw only sometimes qualifies as sci-fi i think those episodes count (something like the shakespeare code, not so much). what he arguably is actually shit at is epic -- he always, always goes for the emotional over the logical, and that can't be sustained with the kind of plot needed to support EPIC.

but anyway i was mostly posting because i felt satisfied that i'd resolved (for myself at least) that he wrote the themes i was seeing in s2 and s3 deliberately. cos that has long bugged me how there's all this brilliant stuff sitting there but then i wasn't quite sure if it was there on purpose or not. like how the doctor/master subtext with pertwee and delgado is probably not there on purpose, but the doctor/master subtext with ten and simm obviously is.