A great deal has been said about this story, so I'll just add that I too liked it; while I still have difficulty deciding between "Genesis of the Daleks" and "The Deadly Assassin" as my favourite story of classic Who, "City of Death" is certainly in my top ten, maybe my top five. Paul Cornell, in the panel that I memorably partly chaired in Dublin in March, singled out Duggan's punch as one of the great moments of Doctor Who, but I'm not sure I can agree: the climactic scenes on the primeval earth actually look a bit naff in comparison to the rest of the story, since they are ostensibly happening outdoors but videotaped rather than filmed. (And as artw pointed out, "Surely the atmosphere would have been unbreathable then?")
And while it would have been nice from a purely plot point of view to have sacrificed some of the padding for a little more exposition at the end, the padding itself is just great to watch. We'll be in Paris next week for a day - looking forward to it!
Edited to add - did anyone else think the incidental music in the first episode had a slight resonace with Gershwin's "An American in Paris"?