Classic science fiction novel with a simple premise: Earth's visitation by extraterrestial beings who are seemingly benevolent and yet secretive in their mission.
This book is both one of the most straightforward and one of the most believable alien fiction books I've ever read. Societal attitudes towards the aliens are varied at the beginning and slowly homogenize as the events of the novel unfold, which seems much more realistic than the typical world-uniting initial hostile reaction to alien ships in other fiction. I also like the fact that the aliens keep their motives secret from humanity. To me, it seems unlikely any civilization sufficiently advanced to master space travel and visit humanity would be hostile to Earth. But it also seems unlikely that even an altruistic alien civilization would simply aid us humans without meddling in our societies. Rest assured, a lot of meddling is done in this novel. The moment the aliens reveal their appearance near the beginning of the second act comes as a shocking revelation. And it is made all the more powerful by the plot developments after the unexpected climax of the novel.