Reddit mentions of Orphanage (Jason Wander Book 1)

Player of Games is a good book, and it's early enough in the Culture series that Banks hadn't yet realized he made the Minds too powerful and doesn't need the human characters to actually do anything. But it is not military science fiction and I don't think it's similar to The Forever War.

If you're looking for more military sci-fi I can recommend Forging Zero, All You Need is Kill, David Weber's Honor Harrington series, Orphanage...and many more I'm sure. Armor is great and I'm sure you've heard of Starship Troopers.

A note on David Weber, I find his overuse of italics a constant irritation when reading his books. It really helps to get digital copies and run them through calibre to eliminate all the italics first.