I would ignore Goldsworthy, given his analysis of the later era Roman army is pretty weak in my opinion.
If you want something that is really detailed in regards to many eras, try A Companion to the Roman Army By Paul Erdkamp. This book does not glorify the Prinicipate era army, which makes it more useful in my opinion.
Google books has a preview for you guys if you want to read it. A preview which is legal.
The sheer amount of information is huge, and it does not give a bias look at the later era Roman army.
Bookmarks