Scalzi has the ability to create flawed but engaging characters you'd want to sit down and have a beer and an argument with. I associate that trait with a few other authors who give public credit to Heinlein for influencing them heavily. Although the subject matter is miles away, the approach to character reminded me slightly of my favourite author, Spider Robinson. John Varley is another who sprang to mind.
The writing is not like Heinlein's, in any of the three cases, but all three authors share that warm interest in human nature. All of them enjoy science and exploring the effects of science, but are more interested in the impact these changes have on people than they are in the technologies themselves.
In many ways, Old Man's War is a riff on or extrapolation of Heinlein's Starship Troopers. A recruiting army uses technology to enhance human capabilities to make them into complete soldiers. But where it is the young, in Heinlein, in Scalzi's world, it is the very old. Attracted by the promise of regained youth, with the only way off planet for many being joining up with the Colonial Defence Forces, John Perry joins up after his beloved wife dies. (She had planned on enlisting as well.)
Once enlisted, he finds himself in the midst of many brutal wars, against many different species. Because those implacably opposed to war would never have enlisted in the first place, there are no pacifists in this book. But there is a lot of thoughtful discussion about war. I hope at some point this series goes on to look at the politics of war - those making decisions who are not involved in the fighting, which the book only hints at. This book is focused on John Perry, the groups of friends he makes when he enlists, The Old Farts, and his experiences along the way.
While it goes along,the book has many interesting meditations about the seat of identity: the brain, the body, brain patterns, and chooses to let that hang in the air as a question rather than trying to definitively answer it. This is one of the strengths of the book - the willingness to not lay down a definitive answer, when the exploration of the idea is so much more interesting.
I enjoyed every minute of reading Old Man's War, and a couple of moments took my breath away. And if I say there was something about the writing style that reminded me pleasantly of my favourite author, you know that's a high compliment.
I read this book as part of an attempt to read all the Hugo Nominees