Oh, good suggestion. It's much more military SF than PHM, but it does have a lot of other similarities, and the series becomes less military focused. It didn't come to mind as something a person would like if they liked PHM, but it probably does fit.

Awesome book, which is part of a series.

Yes this is a good one.

Came here for this. Great story.

I have a love/hate reaction to this suggestion.

Love - It's a great book!

Hate - I've read it already, and I came here hoping for ideas of new books to read!

This is getting away from the hard science of Project Hail Mary but if you like Old Man's War check out the Interdependency Series. It's a bit funnier.