玩命 always has negative connotation. Other netters have already explained.
If you want to mean a "fun life," you would say 快樂人生. To describe someone who lives a fun life, you would say he 遊戲人生.
There are subtle differences between 命 (including 生命, 性命, and 人命) and 人生, even though both are translated as "life" in English. A 命 is saved or lost, while a 人生 is fulfilled or ruined.
If you want to mean a "fun life," you would say 快樂人生. To describe someone who lives a fun life, you would say he 遊戲人生.
There are subtle differences between 命 (including 生命, 性命, and 人命) and 人生, even though both are translated as "life" in English. A 命 is saved or lost, while a 人生 is fulfilled or ruined.