This summer I've been playing games on iOS more than usual.
I'm sure I am going to leave a lot of worthy games behind1, but there are three that I have been playing a lot lately and feel like you should check them out too.
The first one has been on the App Store for quite some time and is called Boson X: it's a running game set in a particle accelerator. You jump right or left by tapping on the screen and straight by holding both thumbs at the same time. It's incredibly difficult (especially the new Dark Energy Containment Laboratory level) but always entertaining and somehow always feels like if you play "just one more time" you will get the score needed to get to the next level.
ALONE is a newly released endless runner that Andrea Latino suggested I tried, and I thank him for that. You are a lonely spaceship in the depths of space and by swiping your thumb up or down you have to stay alive by avoiding rocks and meteors (I immediately disabled the inverted controls). The game is hard and frantic and I didn't get this excited for an endless runner since Canabalt and that's saying a lot. The controls, once you get used to them, are perfect and both the art direction and music are top notch.
It would seem that my last suggestion, Rules, would be an easier and more relaxing game since you need memory and thinking more than reflexes and skills: quite the contrary. It's incredibly hard to get past levels ~20 but it's also extremely rewarding and you will always find yourself trying to get past your best score or your highest level. Good luck!
Hope you enjoy these games and I'm open to your suggestions, would love to try some new games out.
You can find them on the App Store (ALONE is also available for Android and Boson X is available for most of the platforms out there):