On signing up John expects genetic modifications to make him young again and able to fight, what he gets is simply beyond his imagination as his mind is transferred to a new enhanced body making him faster, stronger and able to do things he could never even of dreamed of.
John Perry is a very likable character, combining the wit, sarcasm and charisma of a 75 year old man with the outlook of a youngster thrust into new and wondrous surroundings.
Once he is shipped out to war we see John and his friends quickly encounter violence, death and loss as war takes its toll, we see light hearted moments and on the other side of the coin grief, remorse and despair.
The story is not over burdened with military action, however. While the war drives the plot, the novel is also at times an emotional love story. John's wife, Kathy, died several years before John joins the CDF. Yet her presence, and John's love for her, are a prominent feature of the story. His memories of her and of their marriage offer a refreshing balance to the horrors faced by the new recruits as each battle they face is different to the last.
Overall I really enjoyed this as Scalzi combines fantastic dialogue and excellent characters with just the right amount of action.