Project Hail Mary is a very enjoyable book. I think overall, I liked it more than The Martian.
The depiction of the discovery of a totally imaginary, scientifically-unlikely organism feels real and... hrm, inventive? Playful? Unforeseen? In a way that is very enjoyable, regardless. The main character stumbles on things, in a way that seems accurate, and avoids the perils of portraying science as a process of mystical intuition or as a process of completely-deliberate experiments. The main guy makes a lot of Fermi estimates. He makes mistakes. And so on.
The character-related twist at the end is quite predictable, but I enjoyed the end of the book nevertheless.
Of course, it's obvious that world governments would not be anywhere near as competent as those in the book in the event of a world destroying emergency. But, well, the plot makes sense in a parallel world where governments make decisions in accordance with reality.