William Wilding's Casual Game Design blog has a wonderful piece on learning curves that I strongly recommend taking a look at. This is a pet topic of mine - it's a non-trivial issue in game design that doesn't recieve enough attention.
He argues (from the point of view of Casual game design) that the player wants to play the game, not learn the rules. With a possible and very specific exception (anyone for whom the Strategic Player archetype is dominant - i.e. players for whom complexity is a key draw), I completely agree, and certainly for games targeting a Casual audience, this tenet should be key!
Sloppy game design (what I call 'kitchen sink' design) throws in every idea it can think of in the hope that gameplay will arise out of chaos emergently. Sometimes it works. If you keep throwing money at it. Better to start with tight design to begin with, though. Thinking in terms of what the player must learn before they get to play is a great way to help keep things simple.