If you are looking for a game that is more in depth you can try Spiral Knights in either your browser or with Steam. It is free to play with levels and equipment that you can trade with other players either directly or thru the auction house ingame. The dungion area can be taken on alone or with others as long as you have enough ingame 'energy' to keep going. The energy will replenish each day or you can buy more so its a fun way to burn some time each day. :)
http://www.spiralknights.com/