Naw, it's the little things. Because of changed pronuciation, case endings were lost in Latin, resulting in a more fixed word order in Romance languages and a fundamentally different grammar. Listen to Chaucer being read aloud in Middle English; it's not some much that words like silly and nice are used differently, but that it is nearly unintelligible what with the vowels all skewed up.

Ceci n'est pas un seing.