He's an incredibly distinguished historian and someone who revolutionized the field of early medieval socio-economic history. His breadth of knowledge is pretty much unparalleled and, while there are many who wouldn't agree with everything he's written (he's very explicitly a Marxist historian), all medievalists would recognise the importance of his contributions.

He also writes for a more general audience than many historians and, while I wouldn't say his work is entertaining as such, it's certainly engaging and informative - I'd recommend The Inheritance of Rome or Medieval Europe to anyone interested in the period.