Project Hail Mary is a big, smart, and deeply entertaining survival story that keeps its focus on one impossible job: save the Earth before it runs out of time. Ryland Grace wakes up alone on a ship with no memory of how he got there, and the story peels back his situation one layer at a time. The mystery works, but the book really takes off when Grace is forced to solve problems with nothing but bad odds, stubbornness, and a growing sense that he may not be alone.
Weir makes the science feel immediate and useful instead of decorative. That is the trick here. Every technical detail is tied to pressure, discovery, or failure.
The humor helps too, giving the book a pulse that keeps it from turning cold. If you like your science fiction clever, hopeful, and built around actual problem solving, this one lands hard.