Features:

Simple, intuitive, and innovative user interface
Every feature and user interface element was designed to be immediately intuitive and quickly learnable without assistance. In order to handle multiple images easily, Paint.NET uses a tabbed document interface. The tabs display a live thumbnail of theimage instead of a text description. This makes navigation very simple and fast.

Layers
Usually only found on expensive or complicated professional software, layers form the basis for a rich image composition experience. You may think of them as a stack of transparency slides that, when viewed together at the same time, form oneimage.

Active Online Community
Paint.NET has an online forum with a friendly, passionate, and ever-expanding community. Be sure to check out the constantly growing list of tutorials and plugins!

Frequently Updated
Updates usually come about every 4 to 8 weeks, and contain new features, performance improvements, and bug fixes. Upgrading to the latest version is very simple, requiring only two clicks of the mouse.

Roadmap and Change Log:

paint.net 4.2.1 - Download, released on August 7th, 2019
This update addes JPEG XR file type support and fixes several important issues and crashes.

New: JPEG XR file type support (Windows 8.1+ required)
Fixed:Holding Ctrl when dragging a selection with Move Selected Pixels will again leave a copy behind (but only with the mouse)
Fixed: crashes when saving DDS images
Fixed: VTF file type plugin. It was not working in 4.2 except for images that were an exact power-of-2 size on each dimension.
Fixed: .BMP files can be opened even if they're not actually BMP images (they still need to be a valid WIC-supported file type such as PNG, JPEG, etc.)
Fixed: very bad performance when opening large images with embedded rotation metadata
Fixed: various crashes, such as when using File->New or Image->Resize, that sometimes happened if the previous update needed a reboot but either 1) it didn't tell you that, or 2) it did but you didn't reboot
Fixed: the problem that was causing the need for the aforementioned reboot in the first place (string resources file was locked by the thumbnail provider shell extension)
Fixed: Text tool will no longer draw tiny text when an image uses dots-per-centimeter instead of dots-per-inch
Fixed: menu ordering of effect plugins that have duplicate names
Fixed: The mouse wheel may now be used to scroll the Palettes menu in the Colors window (thanks @AndrewDavid for the suggestion and @toe_head2001 for the fix!)
Fixed: metadata handling that was preventing some images with EXIF tag 330 from being able to load
Fixed: metadata preservation for old images that pad EXIF string values with null terminators
Fixed: title bar text color when using certain custom accent colors in Windows 10
Fixed: title bar accent color when Tablet Mode is enabled