My first Simak novel I was quite impressed. The first half of the book is setting up the situation, back story and character. The plot only begins to unfold in the second half.
The book culminates in a global and (unbeknownst to the rest of humanity) a galactic crisis at which the protagonist Enoch Wallace finds himself the centre of.
Enoch single handedly mans a way station on a galactic highway in which a galactic confedation of alien beings traverse at faster than light speeds, that have technologies, sciences and systems of logic and mathematics far more advanced than our own. Meanwhile the rest of humanity (set in 60's America) is oblivious of the existance of extraterrestial life, as well as the way station, seems on the brink of all out war that threatens to wipe out most of the human race. The galactic civilization has it's own problems and is reaching it's own crisis point.
The continued existance of earth's way station, and perhaps earth's salvation for the future, is threatened and Enoch is faced with with an impossible dilemma and the fate of humanity as well as the galactic confederation rests with him.
There are a lot of themes and ideas touched upon in this book that will give you plenty to think about.