Very strongly-starred review for me partially due to nostaliga goggles, as this was my first Imperial Guard codex, a Warhammer 40,000 (model wargame) faction I have kept as my main focus ever since, so this book has had a great influence on the direction of my life and friendships.
The book itself is very slim, as all 3rd Edition Codexes were, but manages to achieve a quite remarkable density of "fluff" (background information and colour, designed to give life to the rules), including a seminal two-page spread of "Regiments" of the Imperial Guard, demonstrating a huge range of imagination-sparkers (such as the Death Korp of Krieg, who have grown to a faction in their own right) and one or two in-jokes (Amerigo Secundus' "Wolverines" regiment).
The beautiful "3D" map of the Conquests of Macharius (Warhammer 40k's Alexander the Great analogue - one of his subordinates is even rather obviously named Arrian!) and the description of how one small Imperial Guard force provides global security to a middling imperial world (including mounting weapons on a river boat, the use of local transport and the presence of an entirely different regiment's support troops due to a clerical error in transit) are masterpieces of short-form fiction deserving of much greater regard.