There are two schools of thought here: total collapse, and transformation.

For the total collapse school, which can be summed up 'everything sucks and is going to hell in a hand basket' read Heather, Goldsworthy, and Bury.

For the transformation, which holds that Rome fell politically but survived and changed culturally into what we understand as early medieval Europe, read The World of Late Antiquity by Brown. Hugely important book in Roman historiography.

HOWEVER, and I can't stress this enough, to really get a grasp on this era you're going to need a strong, unbiased understanding of the Huns. For that you'll need to read Empires of the Silk Road by Beckwith (totally changed how I understand Eurasian history) and the Cambridge History of Inner Asia Volume I (can be pricy, but shop around on Amazon and you can find a copy somewhere usually for like...30 bucks).

Have fun!