No spoilers here, read on with impunity.
Like The Martian, this is another astronaut-up-the-creek-whittles-own-paddle story. The stakes this time are higher, much higher, and then they unexpectedly double. The protagonist, interestingly named Dr. Grace (heh), isn't quite the square-jawed astrohero of The Martian, but he rises to the occasion – just as soon as he can remember his name.
Other things to note, without spoiling anyone's read... The whole book has some very somber undertones that were not there in Weir's two earlier novels, the above-mentioned The Martian and elsewhere-reviewed Artemis. Still, it has the same comfortable nerdy wisecracks we've come to expect, and it's a fast and fun read. "OK, how's he going to get out of this new fix now?" is the question of every chapter, and the payoffs all along the way keep things moving. Some parts are downright misanthropic. Namely, Grace's last academic paper is a giant glowing screw-you to colleagues in his former and future field. That's just unprofessional and petty, even if we are largely in sympathy with Grace given the situation. When this is followed by Grace's ultimate situation (no spoilers!), you can feel the warm glow of animosity that simmers throughout the book. This slight flaw makes for a more interesting character, not the cheap perfection that Grace could have been in the hands of a less capable author. Ultimately though, Grace re-finds his real calling in the last pages. Finally, there are two big items that are never explained, but are merely science-y MacGuffins – I promised no spoilers, but this will get close; hang in there – a fully miraculous material and the coating on the central mystery of the book. I don't quite buy either one, but I was having such a good time reading that it didn't matter all that much.
Eh, if you enjoyed The Martian you'll enjoy this one too. Finally, rumor has it that there's a movie in the works. Ought to be good.