The Development of Braid

Gamasutra sat down with Jonathan Blow, creator of the successful independent game Braid. He talks about going through the three-year-plus development cycle as a one-man team, and how his concept of the game changed as he worked on it. He also discusses what he feels is the difference between "natural rewards" and "artificial rewards."
"... for the most part, when you're playing Tetris, you're enjoying it because you enjoy fitting the blocks together. Whereas when you play World of Warcraft — and what I'm about to say is a generalization, since different players enjoy different things, obviously — a lot of the appeal of playing World of Warcraft is not in the core gameplay mechanic, because it's boring, a lot of the time. ... I think what keeps them in there is, at first, the level ding, because it's very addictive to get that. 'Okay, I've got more gold. Whatever.' And eventually, they've made this huge time investment and they've got a character there and they know what that level ding feels like and the next one is pretty far off, but they can get there! And it's not any better, because this is like number 67. It's got to be better than 66!"

http://games.slashdot.org/article.pl.../09/13/1723229