This story strongly impressed me the first time I read it, and it impressed me again. It remains consistently one of my favorites, and most memorable, in the book. The concept of writing about humans in a far future is neat, and it's really neat that they have moved beyond flashy cities into quiet, comfortable suburban living, but have even more power!
What I notice this time more than I remember is the long discussion about massive size and power of both the visitors' star ship and the abandoned city. Also this time I notice the plot device of having the protagonist being a generalist who observes, not a specialist with a mission.
A Technofiction flaw is that the big ship lands on earth, it doesn't send down a shuttle, and later, the fleet of huge ships hover over the city. At the time of this writing rocketry being thought of as an interstellar travel tool was only a decade old so its benefits and limitations were not well understood. Likewise, the concept of atomic power was about a decade old as well and equally not well understood.
A second technofiction flaw is that the city buildings survive so well -- for millions of years. Campbell tries to explain this off as a byproduct of how advanced the builders' technology was, but I don't buy it. If the builders' technology was advanced, the buildings would be efficient -- cheap to build but not long-lasting. But while it may not be right, the description of the city is neat! A related technofiction flaw, in millions of years these inhabitants would be a new species, not even neo humans anymore. It's a classic writer's flaw of tossing about too big numbers.
But Campbell really does try to get a handle on both "big" and "long" in this, and to help that he uses a planet-forming concept that was briefly quite popular -- that the sun's planets formed as the result of a near-miss between the sun and another star. It's a concept I'd nearly forgotten about now forty years later. But this concept was popular in the first half of the 20th century in part because it made planets quite rare, which made life quite rare, which made Christian theologians like the theory a lot. Campbell takes this concept one step further. He has the alien's star be the Sun's twin that did the ripping, and then both orbited separately around the galaxy until they were now relatively close to each other again. Whew! Nice big! Nice long!
Campbell does do a nice job of upping the energy sources for the three eras: the visiting aliens use atomics, the city builders use something that wraps through space and time, and the current Earth folk use something even more spacetime twisty. He also mixes in a bit of relativity when he has the future human cut bait on the colonists when they return and announce they will be running earth now. The future human ships their whole fleet back to their home planet, poof!, and although their journey took years, they arrive back home just a year after they left due to relativity-twisting. It's a neat flashy display of patronizing power!, but the relativity twisting aspect doesn't work quite as well for me.
I also like his motivations for the future earth people -- in these visiting aliens they are dealing with primitive, rambunctious, children, and they deal with them kindly. In the end they tell them, gently, "Get off our lawn."
Another feature I noted reading this time was the regimented nature of the crew. This was clearly showing ocean-going ship social features, and clearly not showing much effect of computerized communication. This is a world structured for where strong backs count for more than strong minds. So, yes, this is another story where the writers have a good grasp of the effects of better transportation, but are completely oblivious to the effects of better communication and computation, and widespread education, automation and prosperity for that matter.