Synonyms for Magnificent:
Formal:
* Splendid
* Grand
* Sublime
* Exquisite
* Impressive
* Magnanimous
* Stately
* Spectacular
* Illustrious
* Resplendent
* Luminous
* Opulent
* Extraordinary
* Remarkable
Informal:
* Awesome
* Brilliant
* Fantastic
* Terrific
* Wonderful
* Stunning
* Gorgeous
* Breathtaking
* Fabulous
* Dazzling
Antonyms for Magnificent:
Formal:
* Mediocre
* Ordinary
* Commonplace
* Dull
* Insignificant
* Unremarkable
* Unimpressive
* Drab
* Humdrum
* Banal
Informal:
* Lame
* Boring
* Awful
* Terrible
* Crappy
* Unappealing
* Uninspiring
* Unremarkable
The best synonym or antonym to use will depend on the specific context of the sentence.