Energetic and full of life:
* Animated
* Brisk
* Bustling
* Dynamic
* Ebullient
* Exuberant
* Spirited
* Vibrant
* Vigorous
Interesting and engaging:
* Captivating
* Engaging
* Entertaining
* Invigorating
* Stimulating
* Thriving
Active and busy:
* Active
* Busy
* Humming
* Rushing
* Thriving
Fun and enjoyable:
* Cheerful
* Joyful
* Merry
* Playful
The best synonym for "lively" will depend on the specific context of your sentence.