Paint.NET is a very good mid-level photo retouching choice with a modern interface
|Very well designed and attractive interface; Looks like some paid editors; Has the best “3D” rotation tool; Many tools clearly separated into Adjustments and Effects.|
|No local help only online; Not really suitable for basic users; Effects and transformations can be slow.|
is a very good mid-level photo retouching choice with a modern interface. It has a nice set of photo correction tools including curves, and levels. My favorite is the Layer Roll / Rotate tool which has 3 axes so it can be used to correct perspective and create some interesting effects.
It has a very nice implementation of layers complete with blending modes, and adjustable opacity/transparency levels. It has a fairly full pallet of selection, painting, and shape drawing tools. It is completed with a selection of filters for adding special effects to your images.
Be aware that some transformations are slow and it requires Microsoft .NET Framework to be installed which it will do automatically.