Here's a great argument that the unifying factor in the most popular iOS games is their controls:
What do all top-selling iPhone games have in common? It’s the controls, stupid.
And the money quote?
What doesn't work so well? Games ported from other platforms often use 'virtual joysticks' or buttons.
We agree with this statement strongly: don't try to emulate a tactile-based control scheme without any tactile feedback!