General:
* Cheerful
* Joyful
* Happy
* Lively
* Vibrant
* Exciting
* Enthusiastic
* Invigorating
* Uplifting
* Inspiring
More specific:
* Bright (for describing a setting)
* Hopeful (for describing a mood)
* Interesting (for describing an experience)
* Productive (for describing a day)
* Energetic (for describing a person)
The best antonym will depend on the specific context in which you are using the word "dreary".