Today i've tried Runescape. Maybe you know it, but for me it was a surprise.
The game is made in Java, so it is OS independent and it is possible to play in Linux.
It is a RPG, with nice graphics and MMORPG (i guess it is right). Beside the RPG, also has some Adventure like actions.
You should give it a try if you like these type of games. Register for free and start playing in your browser.
- Install JAVA - In ubuntu or derivatives - sudo apt-get install sun-java6-plugin
- Go to website http://www.runescape.com/ register and play!!!
Play it, it has a nice tutorial, and is a lot of easy and fun.