Pixelmator provides most of the photo-editing tools you would need for personal use. Unless you require industrial-strength capabilities, Pixelmator should meet your requirements.
Wide range of effects: Pixelmator offers a broad collection of selection and effects tools, from blur and distortion to sharpening and retouching.
Painting and drawing: You have lots of control over brushes and can set size, opacity, and angle, for example. The tool also supports Adobe Photoshop brushes.
Layers: Pixelmator handles layers and lets you duplicate, delete, rename, and hide layers.
Color correction: You can choose to auto-enhance an image or fine-tune it with a collection of color-correction tools.
Companion iPad and iPhone apps: Pixelmator is available on OS X and also iOS. Through iCloud, you can edit and sync images with the OS X and iOS Pixelmator apps.
Gloomy interface: The tool's interface is dark, and while some might say it looks striking, with a similar feel to Apple's Photos app for OS X, the look can also start to feel dreary.
While Pixelmator lacks Adobe Photoshop's breadth of professional-level tools, it is still a solid choice for your day-to-day image-editing tasks on the Mac.