How good can a story be before its bad aspects are excusable?

The Talons Of Weng-Chiang
is notable for many things — it’s the last story for Philip Hinchcliffe as producer (and he let the show go so far over budget to make it a good one that the budget was slashed for future series…), it’s the last story that David Maloney ever directed for the show, it’s one of Robert Holmes’ best scripts — but there are two things that make it especially notable — the blatant racism, and the terrible special effect of a rat