Would it be too much to ask for an overview of Dark Ages (5th to 10th century AD) feudalism in Europe as well as a general overview of feudalism during the High Middle Ages (before the plagues) in England, France, Holy Roman Empire, Byzantine Empire and Italian states?
Yes, this would be too broad a spectrum to ask. However, overviews of the Dark Ages as well as overviews of the problems of "feudalism" as a term are very popular posts, and a quick search will probably turn up the answers you're looking for.