I am always on the prowl for something a little different in a photo editor, and Truefilm (US$0.99) meets the requirements with a comprehensive suite of tools at a low price. The emphasis in this app is on making changes quickly and having a complete ability to go back and try things again.
There are the usual adjustments for photos, but they go deeper than a lot of editors. You can play with color temperature and balance, there is an effective clarity tool for sharpening, selective blur and a patch tool for removing blemishes. The latter isn't something you usually see in an iOS editor. Crop tools are one tap away in a variety of aspect ratios and you can create your own cropping shapes.
Truefilm provides a wide variety of frames and some useful filters that are subtle rather than garish. There are also some black and white transformations. Text can be added with various colors and levels of transparency.