Formal:
* La vie est belle. (This is the most literal and formal translation.)
* La vie est bonne. (Slightly less formal than "belle", but still polite.)
Informal:
* La vie est cool. (This is a more casual and modern way to say it.)
* La vie est géniale. (Similar to "cool," but with a slightly stronger emphasis on positive emotions.)
* J'aime la vie. (This translates to "I like life," implying a positive feeling about it.)
* Ça va bien. (This literally means "It's going well," and can be used to express that life is good in general.)
The best way to say "life is good" in French depends on the context and your personal style.