Mezamashii can also have the meaning of Brilliant, and many Japanese-English dictionary say so, but I think this word is rather used to describe "noticeable" or "marked" change in a positive direction. For example, the sentence "a marked improvement" can be said "めざましい進歩(Mezamashii Sinpo)" in Japanese. Unlike the word Brilliant, you can't use Mezamashii with anything haven't changed. When you want to talk about some static matters, you'd better to use what I have answered.