Catherine Tate. Story is both traditional and, it must be said, very silly. But the humour, action and music aspects are superb. Tate is astonishingly good and the meeting between Donna and The Doctor (which was cleverly delayed in the script) is surely one of the greatest moments in DW. Likewise the strange/sudden appearance of Rose. Huh?!
Shame about the babies made from fat, though. A silly 8/10.