The widely accepted definition of unique is “one of a kind.” Thus, avoid modifying it with words such as very, quite, and so on. Many language experts object to sentences such as the following:
The company’s new advertising campaign is very unique.
Why is this phrasing a problem? Because, the argument goes, either something is one of a kind, or it isn’t. It can’t be almost one of a kind, or extremely one of a kind. Even though one often hears unique used colloquially in the sense of “unusual” or “remarkable,” this usage is not broadly accepted as standard.
Apart from the grammatical perspective, there is a stylistic issue here as well: the sentence above simply sounds better and reads more powerfully without the very.
The company’s new advertising campaign is unique.