Picture++ is a sophisticated picture enhancement extension for Photos.
It will analyse the image and make an image-specific enhancement.
The amount of enhancement can be controlled with a single slider from 0 to 100%.
The relative amount of each individual enhancement step (auto brightness, more color and sunny faces) can also be set.

The Picture++ application itself (outside Photos) can also open, improve, and save most RAW, HDR and other image file formats to JPG and hence serves as a RAW to JPG converter. It can also open folders and has a slideshow to automatically navigate to the next picture.