Kingdom of Loathing - My new addiction.

For something with so rudimentary an interface (in contrast with console dungeon crawlers) this is one of the most fun and compelling games I have played in a while.  

http://www.kingdomofloathing.com/

I would suggest a look at the wiki as well.. Should you do the right thing (start playing KoL) the wiki will prove invaluable.  http://kol.coldfront.net/thekolwiki/index.php/Main_Page

From their wiki:

KoL's designers have cleverly created a scheme for keeping your interest long past when you have 'won'. Once you beat the main quest, you can ascend and restart the game as any class. You start over as a level 1 character, and your items are put into a storage locker to which you will have restricted access. There are several choices to make when ascending, such as do you want your next life to be easy, or would you like to take on some voluntary restrictions and challenges in order to receive better rewards? Many items, trophies, adventures and areas are ONLY available ascended players that have given themselves restrictions. There are a variety of fun ways to play out your next life, and you can try them all!

When you ascend you will have the option to keep one of your skills from your current life to be permanently usable for all other incarnations. Hence, you can continue to build up your character by cherry picking skills from all 6 classes!

Ascension is fairly complicated, so be sure to read through the details before you shuffle off this mortal coil. Once you start ascending, if you are looking for strategy tips, you can try asking on the forums, or check Ascension Strategy for normal ascensions or Hardcore Strategy for hardcore ascensions. (Specific advice on those two pages can become outdated quickly, but the general advice is useful.)