I didn't find it in the book list on the sidebar. Apologies if this is the wrong sub reddit.
It was from the perspective of several campaigns in to the nation. The book did a good job of painting a picture of the relevant cast of characters as well as immersive descriptions of socio-economic life.
I believe it was published in the aughts. It was the only history book that read "cinematically" for me. Read it all in one sitting and put it back on the shelf at barnes and noble (sorry B&N).
That sounds a bit like Peter Heather to me. Perhaps The Fall of the Roman Empire or Empires and Barbarians?
Since you've got some background, you might want to look at Guy Halsall's Barbarian Migrations and the Roman West or Peter Brown's Rise of Western Christendom. Bryan Ward-Perkin's Fall of Rome and the End of Civilization is also well known.
It's worth remembering that these are high-stakes arguments sometimes built on slender evidence. I think Halsall does the best of the authors mentioned at showing what exactly he's working with, giving the reader an honest insight into the historian's laboratory. (His Worlds of Arthur is an excellent such example.) If you've got the time and interest, read the author and his critics!