Hey, I missed this thread, must have sneaked it in while I was busy.
Whilst I actually write and publish my own games for iOS, I'm not really into the kind of game you are talking about and so don't play them that much.
What I can testify is that the underlying horsepower, of CPU and GPU, in iOS devices, is pretty amazing. I recently wrote my own OpenGL 3d engine (in Apple's 'Objective C'), with 'photo real' rendering and 3D manipulation of multiple moving pieces in a puzzle game. I'd never done any serious CG work before and so fully expected that I'd need to go back and spend vast effort optimising the graphics interface, physics and motion handling code to get it too run in the 16mS needed for 60 frames per second rendering. I even thought I might have to admit defeat and employ one of the commercial games engines. But no need... my first crude cut of code, full of ugly maths trig functions, ran easily at full rendering rates. Now imagine what a team of highly paid graphics gurus, from one of the big studios, might achieve...?
Per actual recommendations, one that a friend who is a good judge of quality plays a lot is 'Hearthstone'
http://us.battle.net/hearthstone/en/ That's the game website, with links to iOS, Android, and PC platforms.
In answer to a question that may arise, 'No', I have no connection whatsoever with publishers or authors of above game.
