A superb small-scale episode, written to perfectly fit the 45 minutes slot, nicely paced, with a great sense of atmosphere, building to a satisfying conclusion. And at the same time developing the Martha/Doctor relationship and giving the fans some nice continuity (recurring monsters, the Doctor repeating Susan’s description of Gallifrey), not to mention the final message of the Face of Boe.
The only (very minor) flaws were, conversely, where things were scaled up: did they really have to take 6 years to cover 10 miles? Convert it to months and it has just as much impact… And the macra have grown as well as devolved. It now looks like a single macra could snap a car in half in once pincer; but half a dozen old-size macra clinging onto the car and trying to prise it open would have been just as scary, and the getaway might have been more credible. But that’s just nitpicking.
The visuals do deserve special mention: they were terrific. The detail of the costumes and the car interiors (the cardigans, lampshades, suits -both pin-stripe and birthday) was a delight, with some great visual jokes (favourite: “meet the kids”). The CGI was exceedingly well used for once; that view from the creepy senate room onto the sun rising behind New New New New etc. York was fantastic.