Much more of a serious work of science fiction than "Silence Please" which was more a story of a prank gone wrong with a little sci-fi in it. As I read the story I wanted to check more and more when it was written. A lot of the ideas that may seem wrong to us now were entirely plausible in 1949, such as:
- Venus being a habitable planet. It's in a decent place to be one, it just so happens that the planet was composed of the perfect ingredients to make a crushing acidic burning hellworld, which wasn't known at the time
- Ice ages being a civilizational threat. The opposite of today's problems, but only due to humans releasing GHGs (largely a theoretical concern at the time), and ice ages could still be a civilizational threat again tens of thousands of years from now (and intentionally burning fossil fuels could be one way to prevent one! Technically we're doing that right now, we've just done way too much way too quickly, and somewhat too early).
- The first moon landing being in the '80s. An altogether more reasonable timeline to anyone who didn't see the US/Soviet space race coming
The beacons certainly didn't seem intended to be hard sci-fi but turned out to be accidentally kind of correct. Today you could build a RIPEG-powered beacon like that - using ionizing radiation to create light which gets converted to electricity and then into radio waves. Photoelectric cells and transmitters aren't exactly filters but they are converting the energy into different forms until radio waves come out.
It's actually totally plausible that the aliens could've had no archaeological evidence to work with, not only due to their limited exploration but the amount of time that had passed and the action of the glaciers grinding everything into sub-glacial debris fields.
I thought the line about the threat of "racial degeneration" (race being used to describe a species by the alien archaeologists) sounded a little eugenicsy, but it's true that civilization reduces evolutionary pressures to maintain and improve health and fitness, medical advancements just more than offset the problem to the point that it's not worth worrying about. We'll be able to easily fix our own genes before we need to worry about them commonly being significantly broken at this rate. Maybe something else that wasn't known at the time, or maybe that was a hint at the twist that was coming...
I thought it was odd that the archaeologist so easily proclaimed that there was no reptilian life on the planet but this was definitely a hint at the big twist. By the time the story talks about the picture closing in on the protagonists's face, I was expecting "That's all folks!" I don't know if it was meant to be anything specific but I was also getting a Donald Duck vibe. If we saw alien kids' cartoons with almost nothing else to go on, we would also seriously consider that they may have been reflecting reality more closely than they actually did.