General Antonyms:
* Remarkable
* Exceptional
* Outstanding
* Noteworthy
* Memorable
* Striking
* Impressive
* Extraordinary
More Specific Antonyms:
* Unique (if the context is about being uncommon or special)
* Distinctive (if the context is about being easily recognizable)
* Notable (if the context is about being worthy of attention)
* Significant (if the context is about being important or impactful)
The best antonym will depend on the specific meaning you want to convey.