In order to fully sum up what City of Death is all about, the easiest thing to do is simply misquote some dialogue from the first scene between The Doctor and Romana: "What City of Death has, - it has an ethos, a life, it has a spirit all of its own. Like a wine, it has a bouquet."
City of Death is one of the all time monumental moments in Doctor Who history, and this is evident after watching only the opening scenes of Episode One. Blissful and romantic, these opening scenes are as adult as the series has ever been, because only adults can look at those opening scenes of Tom Baker and Lalla Ward, clearly falling in love, dodging Parisian traffic to the strains of Dudley Simpson's most wonderful score ever, and fully understand what a fantastic achievement this story is. Only Doctor Who could cut from an exploding spaceship piloted by a spaghetti-headed monster 400 million years in the past to two Time Lords riding a subway in Paris, 1979, and get away with it.
Parts of this episode may look like they were commissioned by the Paris tourist bureau, but the effort to take Doctor Who overseas for the first is 100% justified by how gorgeous it all looks. The scenery, the acting, the most fantastic script from Douglas Adams (to quote a few more of the tremendous lines from this episode would only do a disservice to the equally brilliant lines that weren't quoted) all add up to 25 of the most enjoyable minutes of Doctor Who I've ever seen.
And we're only at Episode One.