Can't play an Online game that requires Java
Apple is automatically disabling old versions of Java for security reasons. If you re-install Java you do certainly run a slight risk of exposing your computer to known "in-the-wild" exploits. This is a decision you are best suited to make. Are the games worth installing Java for? Are there alternate places to play the same games without using Java?

If you need to install Java, follow this link to get the latest version.