Pixelmator is a great image editor on iPhone, iPad an Mac. I've tried it when I was looking for a less comprehensive an expensive alternative for Photoshop.
It has almost al basic functions of an image editing app. Layers, blending, formatting and color adjustments are all there. It also works seamless with the MacOS and iOS environment.
The only desires I have for this app are a decent cropping tool and somehow less tapping to get to all the tools (it can take quit a few taps to make certain layer adjustments)
Great work from the Pixelmator team