From my answer to a similar question a while ago:

'Gothic' is a term we receive from the Italian renaissance and then further embellished as a pejorative in the subsequent two centuries. Gothic stems from the 'goths', or barbarians, which various renaissance and baroque historians used to refer to the 'dark ages': these historians were enamoured of classicism and Roman effects and as such viewed the entire middle ages as a dark age, as a negative moment, of creativity and learning; as an overtaking of progressive, higher culture by barbarians.

While to us now the term has lost its negative elements, when it was first used in the 16-18th century it was entirely a criticism of the deepest sort and which still lives with us in terms like 'dark ages'.