I understand that what we is describe as Feudalism was the description of a society (Neapolitan I think) in a particular short time period. How does the society in Medieval Europe differ from this particular system to warrant such a dislike from the academics?
This is a complex topic, and it would be more true to say that medievalists caution against using the term without care, definition and qualification than it is to suggest they "dislike" it absolutely. Fortunately, however, the AskHistorians FAQ is here to help. We have a section addressing these problems and, while there is always more to say, you might like to check out those resources while you wait for fresh responses to your query.