I love the controlls for Diablo 3.  They start out slow: the first step is literally just to click a zombie.  Then you click 2 zombies, then 4, 8.  I think you could estimate the strength of monsters per minute through the whole experience and it would be exponential until the end.  Roughly.

And as more powerful monsters are introduced, so comes player power.  Player power comes mainly from items and skills.  But you don't start with 20 skills and 100 runes.  You don't even start out with a right click.  The beginning is just left click and just one zombie.  As you gain more power, you gain new keys, one by one.  It's a beautiful demonstration of the lessons learned from WoW.  First thing is pyro mode:  You start out as a little tadpole who just left clicks things to death.  You end up as a whirling death ninja swiftly cutting through hordes of rediculously lethal foes.

It's a progression not only in character or visual appearance or even player skill, but in the interactivity of the game itself.  The progression is so baked in that the game itself is gated upon it.  And I think that's great.