Playing games is important, at least that is my justification for spending so much time on Mount&Blade Warband: cRPG mod. The most addictive games are going to have a learning curve, and there is one here. If you've never played it, it is available on steam and often on sale - you will not be dissapointed.
Unfortunately all this research is keeping me from being more productive, as this game/mod usually does for periods of time. Why?
Well, it's multiplayer with a solid base of veteran players, a unique, fun and frustrating control system, and the mod adds enough variety and character building for people who like that sort of thing. Also, it is medieval combat - nothing like smashing someone in the face with a morning star to brighten your day. Err, this is not a game for children.
There have been attempts to replicate this medieval combat with UDK, though nothing strikes me as near complete or playable. Which is probably why it still has a loyal fan base.