Fun in games

While bopping around Ludology.org and following some of the links in the blogroll, I came across this post and the following quote really struck me as interesting:

"Games are pleasurable because they are rule-based, because they are well-defined (and definable). It is the formal nature of games that makes them fun."

What do you think about that?

Also, just what is ludology? I've noticed a lot of references to it.