Formal:
* Великолепный (velikolepnyy): This is a good choice for describing something impressive or grand, like a building or a performance. It carries a sense of splendor and magnificence.
Informal:
* Отпад (otpad): This is a slang term that means "awesome" or "amazing." It's very colloquial and used primarily by young people.
* Классный (klassnyy): This means "cool" or "great" and is a more general term for something good.
* Шикарный (shikarnyy): This means "chic" or "stylish," and is often used to describe something luxurious or elegant.
* Прекрасный (prekrasnyy): This is a more poetic word for "beautiful" or "wonderful," but can also be used to describe something amazing.
Contextual:
* If you are talking about a person's appearance, you could say "Она выглядит потрясающе" (Ona vyglyadit potriasayushche) which means "She looks amazing."
* If you are talking about a party, you could say "Вечеринка была великолепна!" (Vecherinke byla velikolepna!) which means "The party was fabulous!"
The best choice for you will depend on the specific context and the level of formality you want to convey.