Kim's thesis is that the Huns have been given short shrift in the scholarship of Late Antiquity. He makes a convincing argument that the Hunnic state was far more organized and powerful than it has traditionally been given credit for.
However, as the book progresses Kim make increasingly incredible claims. He makes the case that every barbarian of consequence was a Hun, including Odoacer, Theodoric, Orestes, and Valamer, among others. He also directly ties the incipient fuedalism of the Frankish state to Hunnic and more generally Inner Asian steppe political organization and even says that the Medieval focus on meat consumption at feasts was a result of steppe influence. And that's not to mention art and diadems and all sorts of other things.
How is Kim's scholarship viewed by the academy? I've found a couple reviews that seem to have the same issues I did:
https://bmcr.brynmawr.edu/2014/2014.03.40/
https://muse.jhu.edu/article/563962
Is this the general consensus?
My exposure to Kim has mostly been through the "comparative empires" field which is dominated by the likes of Walter Schiedel; within this field, Kim was an editor for Eurasian Empires in Antiquity and the Early Middle Ages: Contact and Exchange between the Graeco-Roman World, Inner Asia and China, a book that I enjoyed greatly and which contains a very abbreviated version of Kim's arguments about the Hunnic origins of some early medieval European concepts and practices. He's certainly a capable and well-informed scholar, but he's also one of the most opinionated with regards to the Huns (a subject that has always been plagued by limited, patchy sources) and I think you can see that reflected in these reviews, which praise his work overall but criticize him for insufficiently supporting his more unorthodox claims. You're right to take his stronger claims (especially regarding Hunnic identity, which is poorly documented and very difficult to reconstruct) with a grain of salt, but he's certainly not a quack or a fraud.