The sport itself:
* Competitive
* Fast-paced
* Strategic
* Skillful
* Athletic
* Energetic
* Exciting
* Intense
* Challenging
* Classic
* Traditional
* Modern (referring to specific techniques or equipment)
The players:
* Talented
* Skilled
* Agile
* Powerful
* Strong
* Fit
* Focused
* Dedicated
* Competitive
* Determined
The game:
* Close (as in a close match)
* Thrilling
* Unpredictable
* Dramatic
* Memorable
* Epic (referring to a particularly long or important match)
The court or equipment:
* Hard (referring to a hard court surface)
* Grass (referring to a grass court surface)
* Clay (referring to a clay court surface)
* Professional (referring to high-quality equipment)
* Modern (referring to new technology used in tennis)
You can also use more general adjectives to describe aspects of tennis, like:
* Fun
* Relaxing
* Social
* Healthy
* Outdoor
* Indoor
Ultimately, the best adjectives to use will depend on the context and what you want to emphasize about tennis.